Results are presented on weight changes in sows which indicate (1) that checks to increases in weight at specific stages appear to be a normal function of pregnancy in sows, (2) that most of the weight gained during pregnancy in excess of that accounted for by the litter and placenta is lost before the next pregnancy, either during lactation or, if this is prevented, immediately after weaning, (3) that considerable weight loss occurs between weaning and re-mating on a level of feeding which is sufficient to allow a mean gain of 1 lb. per day during pregnancy, and (4) that sows given a relatively low level of total feed during lactation appear to lose considerably less weight between weaning and re-mating, and to gain weight more rapidly during the first few weeks of pregnancy, than those fed to a relatively high level during lactation. Practical implications of these results are considered.