1. Male Wistar rats were allocated at birth to foster mothers in litters of three, nine or sixteen. At weaning animals from each litter size were ad lib.-fed on a stock diet. Further animals from litters of nine and sixteen were fed on the stock diet in restricted amounts until 12 weeks of age and then rehabilitated by being allowed ad lib. access to the stock diet.
2. Five animals from each group were killed at 24 weeks of age and the size and number of cells determined in four specific fat depots.
3. Animals reared in litters of sixteen and further undernourished from 3 to 12 weeks (group L16/U) had significantly fewer fat cells at all sites studied than animals reared in litters of three and ad lib.-fed. Group L16/U animals also had significantly fewer observable fat cells at the epididymal site than ad lib.-fed animals reared in litters of nine. These results differ from those found in the Black and White Hooded rat where, after similar treatments, no significant differences in observable fat cell number were found.