Four normal subjects and 54 growth hormone (GH)-deficient patients including 43 children with growth failure were given an intravenous bolus of growth hormone-releasing factor (GHRF). Plasma prolactin (Prl) and GH after GHRF were studied. Basal plasma Prl was either normal or elevated and could not predict the GH response to GHRF. A correlation was found, within the group with basal hyperprolactinemia, between basal Prl and the net Prl increase after GHRF. No correlation was found between the net GH and the net Prl increase after GHRF. Plasma Prl was significantly, although weakly, increased after GHRF in the normal subjects.