To evaluate the effect of chronic suppression of somatostatin during treatment with GHRH, we studied in a double-blind and cross-over study 13 prepubertal children with growth hormone deficiency (7F, 6M) ages 3 11/12 to 16 8/12 years. Each patient was studied prior to, and 12 and 24 months after starting treatment to determine plasma GH concentrations every 20 minutes during 24 hours, IGF-1 and IGFBP-3. Height was measured every 6 months. Treatment consisted of GHRH 20 ug/Kg/day sc + atenolol 1 mg/Kg/day or placebo during 12 months. Patients crossed over to the alternative treatment during the following 12 months. Spontaneous GH concentrations were analized by the Pulsar method. Results are shown in the table.Conclusions: 1. -Chronic blockade of somatostatin secretion enhances growth velocity during the first year of GHRH treatment. 2. -There is a tendency for the mean GH concentration to be greater in the group treated with atenolol, but this does not reach statistical significance. 3. -There is no significant difference in plasma IGF-1 and IGFBP-3 between the groups treated with GHRH plus atenolol or GHRH plus placebo.