The status of growth hormone (GH) secretion together with the effect of GH therapy was studied in six children with achondroplasia. One patient had impaired GH secretion, which may, in part, be due to obesity. The pre-GH-treatment height velocity was 3.8±0.7 cm/year, but this increased to 6.0±1.0 cm/year in the first year of treatment and to 4.4±0.6 cm/year in the second year. One patient who underwent GH therapy for 4 years showed good response in height velocity. A considerable variation was observed in response to GH therapy within the treated cases.