A total of 47 prepubertal children with hGH deficiency were treated for up to 6 months with recombinant somatropin. All the children markedly increased their growth rate; 21 of them were naïve (not previously treated with hGH), and increased their growth rate from 4.2 +/- 0.2 cm/year to 13.9 +/- 0.9 cm/year (calculated from growth data after 6 months' treatment, n = 11). Of the 47 children, 26 had been previously treated for 2 +/- 0.3 years (range 0.3-8.3 years) with pituitary hGH. After a period of 0.9 +/- 0.03 years (range 5-15 months) without any hGH therapy, their growth rate increased from 2.9 cm/year to 11.1 cm/year on recombinant somatropin therapy (calculated from growth data after 6 months' treatment, n = 10). One child reacted with temporary local erythema at the injection site. Anti-hGH antibodies, with a binding capacity of 0.02 mg/litre, were detected in 1 of the 16 children after 6 months of therapy. No adverse effect on her growth rate was seen. No changes in levels of antibodies to Escherichia coli proteins were detected. No other allergic manifestations or systemic side-effects were demonstrable.