Plasma cortisol and platelet serotonin (5-hydroxytryptamine, 5-HT) concentrations were determined in 39 male psychotic and 39 male non-psychotic depressed inpatients, and in 69 male healthy control subjects. Psychotic or non-psychotic depressed patients had higher predexamethasone plasma cortisol levels than found in the control group. After the dexamethasone suppression test (DST), psychotic and non-psychotic depressed patients were subdivided into suppressors and non-suppressors. Psychotic and non-psychotic patients had significantly different platelet 5-HT concentrations among themselves and compared with the control group. However, there was no significant correlation between plasma cortisol levels and platelet 5-HT concentrations. Dexamethasone administration did not affect platelet 5-HT concentrations within subtypes of depressed patients. Abnormal cortisol suppression after the DST occurred more frequently in psychotic than in non-psychotic patients. Platelet 5-HT and plasma cortisol concentrations were decreased in patients with pronounced suicidal behaviour. Our results suggest that plasma cortisol and platelet 5-HT concentrations might serve as independent biological markers for different subtypes of depression.