Pregnant Swiss albino mice were whole-body exposed to 250, 150 and 50 R gamma-radiation from 60Co in the presence or absence of 2-mercaptopropionylglycine during selective organogenesis and fetal growth periods (days 11.25 and 14.25, 16.25 and 18.25 after conception, respectively). Both the protected and nonprotected pregnant females of 11.25-day gestation showed complete resorption of embryos irradiated with 250 R. With 150 R, in absence of the drug, 11.25-day gestating females showed partial resorption (76.10%). The percentage of parturition improved in the drug-treated females. Nonprotected females irradiated with 50 R showed slight resorption, while drug-treated females had normal parturition. Females irradiated during the fetal growth period showed no resorption. Also, no significant alteration in litter size and sex ratio of the newborn animals was noticed when irradiated during this period, both in the control and the experimental groups. Mortality of the young was higher in nonprotected animals as compared to the protected ones.