A 32-year-old Caucasian male, clinically euthyroid, with paranoid schizophrenia and granulocytopenia, had elevated total and free serum T4 and T3; serum TSH was normal (2.7 +/- 0.7 micronU/ml). There was no goitre present, no evidence of Graves' disease, and no evidence of pituitary tumour. He had a normal response to methyl-TRH, with a TSH increment of 14.6 micronU/ml, T3 increment of 212 ng/dl, and T4 increment of 4.7 microgram/dl; baseline value and decreased the TSH increment in response to methyl-TRH. T3 therapy (100 microgram/day) decreased the thyroidal radioactive iodine uptake to less than half the baseline prolactin was normal with a normal response to methyl-TRH to 4.1 micronU/ml. Iodine therapy caused an increase in his baseline TSH with an increase in the TSH response to TSH. The metabolic clearance rates (MCR) and production rates (PR) of T3 and T4 were increased. Baseline serum levels of glycoprotein hormone alpha-subunit were normal and showed a slight increase in response to methyl-TRH, similar to normal subjects. This patient has evidence of partial pituitary and peripheral resistance to thyroid hormone; his only evidence for hyperthyroidism is the elevated MCR and PR of T3 and T4.