Twenty patients with a major depressive disorder and 20 control subjects were subjected to a 1 mg dexamethasone suppression test (DST) and a challenge with intravenous (IV) methylphenidate (MP)(0·3 mg/kg). None of the controls, but 9 depressives, were DST non-suppressors. Among the depressives there were correlations between DST-cortisol and baseline (4 p.m.) levels of cortisol, growth hormone, prolactin and adrenaline. Compared with the controls the depressives had a decreased cortisol response and an enhanced adrenaline response to the MP challenge. The decreased cortisol response was not related to either DST-cortisol or baseline cortisol, but was correlated with the mood response to MP.