The effect of several types of tactile stimulation on ornithine decarboxylase (ODC) activity and serum growth hormone (GH) levels was studied in maternally deprived rat pups. Previous experiments have shown maternal deprivation to be associated in rat pups with a significant decrease in serum GH and in the level of ODC activity in brain, heart, and liver. In the present study we have found that vigorous tactile stimulation of the pups using a moistened brush completely prevented these effects of maternal deprivation, while other forms of tactile stimulation, light stroking with a brush and tail pinching, were ineffective. Vigorous tactile stimulation was also effective in raising GH and ODC levels previously lowered by 2 hours of maternal deprivation. We conclude that vigorous tactile stimulation in the form of active maternal behavior is essential for the maintenance of normal serum GH and tissue ODC activity in neonatal rat pups. © 1980.