We have studied the effect of varying doses of biosynthetic human GH on the growth response over the first year of therapy in 90 short prepubertal children (67 males and 23 females, aged 3.1-12.9 years). As pretreatment height velocity was the predominant determinant of response, the children were divided into three groups on the basis of their pretreatment height velocity standard deviation scores (SDS). Group A (n = 27) had pretreatment height velocity SDS between +1.3 and -0.8 (short normal growing children), group B (n = 35) between -0.9 and -2.0 (moderate GH insufficiency) and group C (n = 28) less than -2 (severe GH insufficiency). Within each group, the dose of GH administered was the dominant factor in the regression. At a mean dose of 16 units/m2 body surface area per week, the change in height velocity SDS over the first year of therapy was +2.9 (95% confidence interval (CI) 2.4, 3.5) in group A, +4.3 (95% CI 3.9, 4.6) in group B and +7.0 (95% CI 6.0, 8.0) in group C. These values translate into increases in growth rate of 2.2, 3.4 and 5.5 cm/year for an 8-year-old in each group respectively. These results have important implications in planning the treatment of children with GH insufficiency.