The cytogenetic effects of erionite treatment of V79 cells were compared with those of UICC crocidolite and UICC chrysotile treatment. A significant reduction in diploid cells with an accompanying increase in aneuploid and polyploid cells was observed with all three treatments. In the erionite-treated cultures, an increase in aneuploidy was observed at all dose levels ranging from 10 to 100 microgram/ml, whereas in the crocidolite and chrysotile-treated cultures, significant increases in aneuploidy were observed at all dose levels except the low dose, 10 microgram/ml. Chromatid aberrations were observed in cultures treated with crocidolite and chrysotile and were especially pronounced at dose 100 microgram/ml of chrysotile. The clastogenic effect of erionite was weaker but statistically significant at dose 100 microgram/ml. An extrapolation of these cytogenetic changes over dose in number of fibers suggests that erionite was more reactive than the other two minerals in producing aneuploidy. The number of fibers required to produce a similar degree of cytogenetic effects was several orders of magnitude higher for chrysotile and crocidolite than erionite.