Female rats were fed diets containing graded levels of pyridoxine throughout gestation. At parturition, the pups were cross-fostered with a dam which had been fed the same diet as the biological mother throughout gestation (an isonutritional foster mother), or with one which had received a control diet containing 400% of the National Research Council recommendations for B6 throughout gestation (a control foster mother), or were left to suckle the biological mother. Physical, neuromotor, and reflexological development of the pups was assessed throughout the 3 week lactation period. There were no significant differences between pups nursed by their biological mothers and by isonutritional foster mothers. Growth, reflex acquisition, and neuromotor activities were impaired in pups subjected to pyridoxine restriction during gestation. Acquisition of a number of reflexes and time spent in neuromotor activities were responsive to cross-fostering with a control foster mother but the deficits were not completely eliminated. Growth was only slightly affected by cross-fostering and acquisition of audicular startle and negative geotaxis was not affected by the nature of the foster mother. The latter reflexes are apparently determined directly by the gestational nutrition of the fetus whereas other reflexes and neuromotor activities are influenced by long-term effects of pyridoxine restriction on the postnatal performance of the dam as a mother, in addition to being directly influenced by maternal diet during gestation.