Twelve hair dye formulations were tested for systemic toxicity by topical application twice weekly for 13 wk to groups of 12 New Zealand white rabbits and for teratologic effects following applications to groups of 20 pregnant Charles River CD rats on days 1, 4, 7, 10, 13, 16, and 19 of gestation. The three semipermanent formulations were applied as is, and the nine oxidation dyes were mixed 1:1 with 6% hydrogen peroxide just prior to application, as in normal use. The formulations induced a broad spectrum of dyes and dye intermediates used or considered useful in oxidative and semipermanent hair color products. In the teratology study no biologically significant soft tissue or skeletal changes were noted. Similarly, the mean numbers of corpora lutea, implantation sites, live fetuses, and resorptions per pregnancy, as well as numbers of litters with resporptions, were not significantly affected by the dye treatment. In the percutaneous toxicity study there was no evidence of compound-induced systemic effects. Microscopic examination of 25 tissues from each animal gave no indication of histomorphologic evidence of toxicity. No dye discoloration of urine was seen at any time during the test or at necropsy. Some of the dye groups showed epidermal hyperplasia, which was probably a reflection of slight irritation due to the frequency of application of the oxidation formulations.