A cytogenetic analysis of peripheral blood lymphocytes of six persons (seven in analysis of chromosome aberrations (CA)) was carried out. The cell cultures were exposed to a constant concentration of positive or negative ions. The exposure time was established as 24 and 72 hours for ions of both signs. In the cultures exposed to positive ions and used for sister-chromatid exchange (SCE) analysis no metaphases were detected. An analysis of cultures after 72 hours of exposition to negative ions revealed an increase in the number of SCE and inhibition of cellular divisions as compared to the control. In CA analysis no differences in the number of aberrations were observed but in cultures exposed to positive ions dicentric chromosomes were detected. Therefore we conclude that the different signs of air-ions had not genotoxic effect.