The in vivo teratology screening procedure described previously was further evaluated using a total of 46 chemicals in 50 different treatment regimens. Pregnant CD-1 mice were generally treated by oral gavage on days 8-12 of gestation at a dose level predicted from a preliminary range finding study to induce a slight degree of maternal toxicity. The effects on early postnatal growth and viability were compared to results generated from standard mouse teratology bioassays as reported in the literature. The procedure correctly categorized 25 of the 30 treatment regimens which were considered developmentally toxic in the mouse, as well as 9 of 11 which were considered to be nondevelopmentally toxic in the mouse. Thus, based upon the criteria used in the present study, the assay correctly classified 83% of the chemicals tested as to their effect in a standard mouse bioassay. (Copyright (c) 1987 Alan R. Liss, Inc.)