Blood levels of polyamines were evaluated in hypopituitary patients after i.m. injection of human growth hormone (hGH). After hGH administration polyamine concentration increased significantly in the first 60 minutes. The concentration of spermidine and spermine increases more in patients previously untreated or treated intermittently with hGH than in patients under continuous treatment. The results suggest that in human as well as in experimental models, polyamines could be involved in the growth process and that hGH probably stimulates polyamine synthesis.