Basic fibroblast growth factor (bFGF) has shown a neuroirophic effect in the neurons of several CNS areas. In vivo, it contributes to restore neurochcmical and morphological deficits in different rodent models of brain damage, including rats with brain damage induced by hypoxia/ischemia when FGF was intramuscularly (i.m.) administered. Toxicological and immunological studies performed in rats, mice and volunteers showed no evidence of side‐effects. Bovine FGF was i.m. administered in children with mental retardation caused by perinatal hypoxia, aged 1–15 years, at dosages of 0–4 or 0–28 μ.g kg−1, once or twice a month, over 7–12 months. Group A [n= 12; 6 treated (T), 6 controls (Ct)], group B (n= 16; 8 T, 8 Ct) and group C (n = 67; 45 T, 22 Ct) were evaluated with the P. A. R. scale, the WISC‐RM and the Gesell scale, respectively. Development increased significantly in treated children from groups A (P < 0.02) and C (P < 0.001), and IQrose by more than 10 points (P < 0.001) in group B patients.