Thyroid function tests (T4, T3RU, free thyroxine index) were performed upon admission in 269 acute psychiatric patients during a 2-year period. Thyroid disease was detected in 3% and euthyroid abnormalities in 9.3%. T4 and free thyroxine index were significantly lower in depressed patients than those with mania or schizophrenia. The rate of abnormal thyroid tests was lower in this study than in previously reported surveys of psychiatric admissions. Laboratory techniques or differences in population may be responsible for the difference. The differences in thyroid function test values between psychiatric diagnoses are relatively new findings, and appear worthy of investigation.