In order to evaluate possible health effects of environmental exposure of humans towards Me mercury species, relevant exposure expts. using Me mercury chloride in aq. soln. and Chinese hamster ovary (CHO) cells were performed. The soln. was monitored for the presence of monomethyl, di-Me and elemental mercury by several anal. techniques including chromatog. as well as at. absorption and mass spectrometric methods. Me mercury induces structural chromosomal aberrations (CA) and sister chromatid exchanges (SCE) in CHO cells. At a concn. of Me mercury in the culture medium of 1.0*10-6 M where the frequencies of CA and SCE are significantly elevated, the intracellular concn. was 1.99*10-16 mol/cell. Possible biochem. processes leading to the cytogenetic effects are discussed together with toxicol. consequences, when humans (e.g. workers at waste deposits) are exposed to environmental concns. of Me mercury.