Abstract Several lines of evidence suggest catecholamine overactivity (noradrenergic and/or dopaminergic) in mania. We studied the growth hormone (GH) response to clonidine (an α-adrenergic agonist) and apomorphine (a dopaminergic agonist) in seven inpatients meeting Research Diagnostic Criteria for mania. They had been completely drug free for at least 3 months before the neuroendocrine procedures and were age- and sex-matched to seven major depressive and seven minor depressive inpatients, drug free for at least 2 weeks. GH was assayed every 20 min for 40 min before and 120 min after either clonidine (0.15 mg i.v.) or apomorphine (0.5 mg s.c.), with an interval of at least 2 days between the tests. The three groups differed significantly in the GH peak response: after clonidine (mean ± SD), 3.2 ± 2.4 ng/ml manics, 3.2 ± 2.4 ng/ml in major depressives, and 13.2 ± 8.7 ng/ml in minor depressives; after apomorphine, 10.5 ± 7.4, 3.2 ± 1.9, and 26.9 ± 15.8, respectively. While there were significant differences between manics and minor depressives and between major and minor depressives after both clonidine and apomorphine, manics did not significantly differ from major depressives on either test. These results do not provide neuroendocrine support to the catecholaminergic hypothesis of manic disorders.