Induction of sister chromatid exchanges (SCEsj in cultures of Chinese hamster ovary cells by 10 anticholinesterase organophosphate insecticides was investigated. The insecticides were two phosphates (dichlorvos and dicrotophos), four sulfur‐containing organophosphates (malathion, parathion, leptophos, and diazinon), and four oxygen analogs of the latter (malaoxon, paraoxon, leptophosoxon, and diazoxonj. All of the compounds except diazinon induced statistically significant increases in SCE frequencies at concentrations between 0.03 and 1.0 mM. These results suggest that SCE induction is a common property of organophosphate insecticides. Compared to the sulfur‐containing organophosphates, the oxygen analogs consistently produced higher SCE frequencies and had stronger antiproliferative activity. Compared to two known genotoxicants, doxorubicin and ethyl methanesulfonate, the ability of organophosphates to produce SCEs is much weaker.