Radiolabelled [UL-14C]-diphenyl sulphide, [UL-14C]-diphenyl sulphoxide and [UL-14C]-diphenyl sulphone were administered by gavage (1.0 mmol/kg body weight) to adult male Wistar rats following an overnight fast. For all compounds, faeces were the major route of excretion of radioactivity (50%). Urinary elimination (40%) was similar during the first (19%) and second (16%) days and a small amount of radioactivity (6%) was found within the carcass after four days. From urinary and faecal data, metabolism occurred via ring hydroxylation with subsequent conjugate formation. Oxidation of the sulphur to form the sulphoxide and sulphone also took place; a small amount of sulphoxide reduction was apparent but no sulphone reduction was found. No evidence for exclusion of the sulphur was obtained, and it appeared unlikely that extensive cleavage of the ring structures occurred.