Fifty-eight short prepubertal children with IUGR received GH treatment (mean dose: 28 IU/m2/week) for a mean (SEM) period of time of 3.4 (0.13) years (range 1-4 years). They were subdivided according to their GH response to a pharmacological test. Twenty-six were GH insufficient (GHI) (group 1) and 32 were non-GHI (group 2). At the commencement of GH therapy mean chronological age was 6.1 (0.4) years in both groups, mean height SDS (SEM) was -3.5 (0.2) in group 1 and -3.6 (0.2) in group 2, mean growth velocity (GV) SDS (SEM) was -1.9 (0.3) in group 1 and -0.3 (0.2) in group 2. GH therapy induced significant growth acceleration throughout the follow-up period without any significant differences between the two groups. GV SDS (SEM) increased to +3.0 (0.5) in group 1 and to +3.7 (0.4) in group 2 (p < 0.05 compared to baseline) during the first year of therapy. Subsequently, the growth-promoting effects of GH therapy diminished with time but GV remained significantly higher than baseline. This growth enhancement produced a significant rise in height SDS (SEM) reaching - 1.4 (0.2) in group 1 and - 1.7 (0.2) in group 2 after 4 years. In conclusion, our data did not show any significant differences in the growth response to GH therapy between GH-sufficient and -insufficient IUGR children who were only distinguishable by their GH secretion. This indicates that the decision to treat a short IUGR child with GH therapy should not be based upon the GH response to a provocative test.