Spermine is a low molecular weight polyamine involved in the postnatal maturation of the small intestine. When administered orally to suckling rats, it induces maturation of the intestinal tract (liver, pancreas and small intestine). Here, we show that this polyamine can induce precocious splenocyte development in suckling rats. In 14-day-old rats which had received spermine orally during 3 days, once daily, we observed modifications in splenocyte population as well as a variation in the proliferation rate of these cells. These observations suggest that spermine might play a role in immune system development. Its effects will be further investigated, namely to evaluate its capacity to enhance defence during the neonatal period.