[en] Systematic observations of radionuclide composition and concentration in the atmosphere have been carried out at the Institute of Physics in Vilnius since 1963. An increase in activity concentration of radionuclides in the atmosphere was observed after nuclear weapon tests and the Chernobyl NPP accident. At present the radiation situation in Lithuania is determined by two main sources of radionuclides, forest fire and resuspension products transferred from highly polluted region of the Ukraine and Belarus. During forest fires the increase in activity concentration of ¹37Cs in the atmosphere was registered in many countries and in Lithuania as well. This work summarizes the experimental data on transport of cesium, plutonium, americium from the highly contaminated territories after the Chernobyl accident. The activity concentrations of ¹37Cs were measured in two - three days samples while plutonium and americium in monthly samples. In addition, the analyses of the events of the increase activity concentration, meteorological situation, speciation of radionuclides and mechanisms of formation and transformation of aerosol carriers of radionuclides are presented. Aerosols were sampled on perchlorvinyl filters and the large volume air samplers with a flow rate from 2400 m³/h to about 6000 m³/h were used. The radiochemical analyses of monthly samples of aerosol ashes (about 30 g) were performed. For separation of Pu isotopes the TOPO/cyclohexane extraction and radiochemical purification using UTEVA resin were performed, Am was separated after TOPO/cyclohexane extraction using TRU and TEVA resins (100-150 μm). ²42Pu and ²43Am were used as tracers in the separation procedure. The alpha spectrometry measurements of Pu and Am isotopes deposited on a stainless steel disc were carried out with the Alphaquattro (Silena) spectrometer. ¹37Cs was determined by gamma-ray spectrometry using the high purity HPGe detector (resolution - 1.9 keV/1.33 Mev, efficiency - 42%). Accuracy and precision of analysis were tested using NIST SRM No 4350B and 4357 as well as in intercomparison runs, organized by the Riso National Laboratory, Denmark. Precision of ¹37Cs measurements by gamma spectrometry was ≤ 7% at 2σ, Pu ≤ 8 %, Am ≤ 10 %. ²40Pu/²39Pu ratio was determined by ICP-MS. For determination of chemical association of radionuclides with aerosol particles the sequential extraction methods were used. Measurements performed in Vilnius and Preila indicated transfer of resuspention and combustion products after the forest and peat bog fires in the Ukraine and Belarus when activity concentrations of ¹37Cs in the atmosphere increased up to 200μBq/m³. The measurements carried out on aerosol samples collected in Vilnius in 1997-1999 indicated the presence of alpha emitting radionuclides. The activity concentrations of ²39,²40Pu and ²41Am ranged from 0.4 to 18 and from 0.3 to 9.7 nBq/m³, respectively. The origin of contamination source was identified using meteorological data of backward trajectories, characteristic speciation, activity and atom ratio of radionuclides. For comparison measurements were performed on aerosol samples collected during the Chernobyl accident and the contaminated Chernobyl soil. In some samples the high activity ratio of ²38Pu/²39,²40Pu up to 0.5 was observed. The presence of the Chernobyl derived plutonium was confirmed by ICPMS (atom ratio ²40Pu/²39Pu up to 0.40 was found). Thus, the Chernobyl accident resulted in contamination of large areas of the Earth's surface and forests by radioactive substances. The redistribution of radionuclides mainly of Cs, from these regions to less contaminated areas takes place during the forest fires, because the aerosol particles generated in a different phase of fire have predominantly a submicronic size and are enriched by the volatile Cs due to its evaporation and condensation on condensation nuclei in the atmosphere (the increase of Cs/Sr and Cs/Pu ratio determined in the forest fire and the laboratory experiments confirms this). A different transformation character of these nuclide carriers is also related to the vaporization of more volatile Cs and its interaction with condensation nuclei after deposition on in the atmosphere and their further coagulation. Measurements performed in Vilnius and Preila in 1992 - 2005 indicated transfer of resuspension and combustion products after the forest and peat bog fires in the Ukraine and Belarus when activity concentrations of ¹37Cs in the atmosphere increased up to 200μBq/m³. The measurements carried out on aerosol samples collected in Vilnius in 1997-1999 indicated the presence of alpha emitting radionuclides. The activity concentrations of ²39,²40Pu and ²41Am ranged from 0.4 to 18 and from 0.3 to 9.7 nBq/m³, respectively. The origin of contamination source was identified using meteorological data of backward trajectories, characteristic speciation, activity and atom ratio of radionuclides. For comparison measurements were performed on aerosol samples collected during the Chernobyl accident and the contaminated Chernobyl soil. In some samples the high activity ratio of ²38Pu/²39,²40Pu up to 0.5 was observed. The presence of the Chernobyl derived plutonium was confirmed by ICPMS (atom ratio ²40Pu/²39Pu up to 0.40 was found)