The growth hormone (GH) and prolactin (PRL) responses following administration of 10 mg i.v. metoclopramide (MCP) ('Maxolon'--Beecham Pharmaceuticals) have been examined in thirty adolescent males with short stature and delayed puberty, either of whom have isolated growth hormone deficiency. The results demonstrate that peak GH and PRL levels following stimulation were highly significantly correlated when all subjects were analysed together (r = 0.61, P < 0.001) but when the responses of the GH deficient and non-deficient groups of subjects were analysed separately no significant correlation was obtained (P > 0.1), this reflected the fact that the PRL response to MCP was significantly lower in the GH deficient group (P < 0.0002). In addition two boys who demonstrated biochemical GH deficiency prior to puberty only, showed PRL responses similar to boys with normal GH reserves. The results suggest that the PRL response to MCP may be of value in the assessment of stimulation tests of GH reserve, as well as in the selection of patients for treatment with GH.