Groups of rats on commercial diet were injected 3,000 IU (group 2) and 7,500 IU (group 3) of vitamin D3 on the 10th day of pregnancy. Compared to control pups (group 1), the pups in group 2 and 3 weighed significantly more on the 10th, 20th and 28th day of age. At 28th day of age, study of the gastrocnemius muscle revealed significantly greater organ weight, protein, DNA and RNA contents, protein/DNA and RNA/DNA ratios in group 2 and 3 pups than in controls. In the liver, whereas all these indices were significantly increased in group 3 pups, only protein/DNA and RNA/DNA ratios were significantly increased in group 2 pups. Brain weight, its RNA content and RNA/DNA ratio were significantly greater in group 2 and 3 pups than in controls. The results suggest that vitamin D administration in pregnancy promotes soft tissue growth in the pups by enhancing cellular proliferation and hypertrophy.