[en] Complete text of publication follows. Magnetic field of 2.25 x 10³ Gauss was applied for 30 minutes, 60 minutes and 90 minutes on the living meristematic cells of Lathyrus sativus L., a leguminous plant and on the bone marrow cells of albino Swiss mice, Mus musculus L. Mitotic indices in meristematic cells of magnetic field treated plants at different times of treatment were found increased compared to those of control sets. Chromosomal abnormalities of magnetic field treated plants were polyteny, aneuploidy, polyploidy, clumping, chromosome erosion and anaphase bridge. Usual aceto-ocein, root tip squash technique was followed in this endeavour. In situ estimation of nuclear DNA in meristematic cells of magnetic field treated Lathyrus sativus plants showed enhanced DNA content compared to those of the control sets. In case of magnetic field treated mice similar increase in mitotic indices in bone marrow cells was found compared to those of the untreated ones following the usual flame-dry technique. Different types of chromosomal aberrations of bone marrow cells of magnetic field treated mice were acentric fragments, clumping, ring chromosomes, chromatid breaks, pulverization, aneuploidy, micronucleus, polyploidy, centric fusion etc. compared to those of the untreated mice. Usual C-banding technique revealed the heterochromatin content of the chromosomes of bone marrow cells in magnetic field treated ones. Centromeric fusion was clearly revealed in this technique. Heterochromatin content was found enhanced in the magnetic field treated bone marrow cells compared to those of untreated ones.