Hypercortisolaemia is a feature of many severe psychiatric illnesses and has been suggested to be both a causal and exacerbating factor of clinical symptoms and neurocognitive impairment. The adrenal steroid dehydroepiandrosterone (DHEA) has antiglucocorticoid properties that may have regulatory effects on glucocorticoid action in the brain. However, there is a paucity of data on these steroids and their ratio in schizophrenia and bipolar disorder. We therefore sought to assess cortisol and DHEA levels and the cortisol-DHEA ratio in patients with schizophrenia (n=20) and bipolar disorder (n=20), on stable medication for a minimum of 6 weeks, and healthy age- and sex-matched control subjects (n=20). Steroid levels were measured from plasma samples collected at 30 min intervals from 1:00 p.m. to 4:00 p.m. Cortisol levels were found to be significantly elevated in both patient groups compared with controls. DHEA levels were elevated in schizophrenic patients compared with bipolar patients and controls, but there was no evidence of a difference in the cortisol-DHEA ratio of the groups. These data suggest that afternoon hypercortisolaemia is evident in symptomatic bipolar and schizophrenic patients compared to controls. However, an elevation in DHEA levels may represent a specific endocrine marker in schizophrenia.