In our previous report on the in vivo cytogenic effect of paraquat, it was concluded that the compound had no mutagenic effect on the bone marrow cells of the mouse (SELYPES et al. 1978). In the first part of this study we investigated whether dlquat would have a mutagenic effect under similar experimental circumstances, and in the second part, we wanted to establish whether the two herbicides, paraquat and diquat, would cause congenital malformations and damage the chromosomes of the embryonic liver cells because, according to published literature data (KHERA et al. 1968, BUS et al. 1975) in the presence of certain parameters they have an embryotoxic effect through the placenta.