In a previous work we have demonstrated that a 65% protein calorie food restriction started during the third trimester of gestation in rats caused a reduced beta cell mass at 4 days of life that persisted until adult age. In this study with adult undernourished (U) rats, we investigated: 1) whether undernutrition affects the beta cell growth potencial and both beta cell proliferation and differentiation, and 2) the implication of the IGFs, highly responsive to nutritional status, in these processes. To this end, we have used the 90% pancreatectomy (Px) procedure in U and control (C) adult rats. The results show that on day 2 after pancreatectomy beta cell replication was significantly higher in C rats whereas the beta cell neogenesis was markedly increased in U/ Px rats. Both the serum levels of IGF 1 and the liver IGF 1 mRNA expression were reduced in adult U rats before and after pancreatectomy as compared to C rats. Pancreatic IGF 1 mRNA expression was reduced in U animals on day 0. However, on day 2 after Px, the increase of pancreatic IGF 1 mRNA expression was significantly higher in U rats than in C. These data suggest that beta cells still have the capacity to regenerate in the adult U rats, with a higher efficiency than controls on day 2 and that both beta cell neogenesis and beta cell replication are stimulated. The increased pancreatic IGF 1 mRNA may be instrumental in these processes.