BACKGROUND: The role of serotonergic system and lipid status in the etiology of mania and its subtypes is not clear. The aims of the study were to determine platelet serotonin (5-HT) concentration, platelet monoamine oxidase (MAO) activity, and serum total cholesterol, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL) and triglycerides (TG) in patients with psychotic and nonpsychotic subtypes of mania and in healthy control subjects. - - - - - METHODS: The serum lipids, platelet 5-HT and MAO were determined in 40 (17 psychotic, 23 nonpsychotic) drug free male inpatients with type I bipolar affective disorder, current episode mania (DSM-IV criteria), and in 32 healthy male subjects. - - - - - RESULTS: Platelet 5-HT levels in manic patients were similar to the values in healthy controls. Serum cholesterol and LDL values were significantly lower in manic patients than in healthy controls. Patients with psychotic features had increased platelet 5-HT concentrations and decreased levels of cholesterol and LDL as compared to the nonpsychotic manic patients and healthy controls. There was no significant difference in age, body mass index, platelet MAO activity, serum levels of TG and HDL between psychotic and nonpsychotic manic patients and healthy subjects. - - - - - LIMITATION: Data on physical activity, dietary habits and alcohol consumption before hospitalization were not collected. - - - - - CONCLUSION: The results of the present study suggest that biological differences between subtypes of mania might depend upon the presence of the psychotic symptoms. Our data confirm our previous results showing the increased platelet 5-HT concentration in psychotic disorders across the different diagnoses.