The efficacy of Genotropin (recombinant somatropin, KabiVitrum AB, Sweden) was analysed in 194 children with GH deficiency, comprising a combined series of four multicentre trials. The linear height velocity increased from 3.3 +/- 1.4 to 9.3 +/- 2.6 cm/year in 149 prepubertal children with 12 months' data available. In 18 pubertal children the pretreatment height velocity was 4.0 +/- 1.2, and increased to 8.4 +/- 1.7 cm/year during 12 months of treatment. There was a positive correlation between the gain in height velocity and the weekly dose of Genotropin. Covariance analysis revealed significantly greater height velocity with 6-7 injections/week compared to 2-3 injections/week; corrections for chronological age, bone age, height SD score and dose were made. On average, a regimen of 6-7 injections/week was 25% more effective than one of 2-3 injections/week corresponding to an extra gain in height velocity of 1.8 +/- 0.6 cm/year. At 12 months, only 0.9% of the children had developed anti-GH antibodies. Very few side-effects have been reported from more than 1000 children on Genotropin.