The ability of rat dams to cope with food restriction as well as a concurrent lactation and pregnancy was examined by varying the duration, time of onset and severity of the food restriction schedule. Groups of females impregnated in the postpartum estrus and nursing 8 pups were either allowed to feed ad lib, given 60% of an ad lib ration from days 1-7, 1-14, 8-14 or 15-21 postpartum or 40% of an ad lib ration from days 1-7. Food restriction regimens that extended through the estimated time of implantation for females nursing 8 pups (days 1-14 and 8-14) resulted in a prolongation of pregnancy. Food restriction in the first week postpartum did not result in a prolongation of pregnancy and did not affect the number of females carrying the pregnancy to term. Dams food restricted in the third week postpartum had pregnancies of the same length as ad lib females but a smaller proportion of this group gave birth to a second litter.