[en] Synergistic effects of quartz dust and of Po-210 have been investigated in lungs and kidneys of rats. The substances (50mg silicone per animal, 5 (or 10)μCi of Po-210 per kg bodyweight) were introduced intratracheally in a single dose. Exposure times were 7 and 12 month. Postmortem the following quantities were determined: weight of lung and kidneys, Po-210 content, hydroxyproline contents of the lungs. Autoradiographic and histopathological investigations were carried out. It was found that synergistic effects increase mortallity. The most frequent cause of death was renal lesions. Po-210 behaves as a nephrotoxic agent, causing damages to all kidney structures, it mainly attacks the epithelium of convoluted renal tubules of nephrons. The cancerogenic effects of Po-210 are enhanced in the presens of quartz. Po-210 predominantly accumulates in the kidney cortex. Po content of lungs and kidneys was still high after 7 month. Po-retention was highest in kidneys not subjected to quartz, in lungs the opposite effect was observed. Hydroxyproline contents are moderately increased in Po-contaminated lungs