Cis-diamminedichloroplatinum II (cisplatin) is an effective and widely used antitumour drug which induces many side-effects. We investigated the potency of dimethyl sulphoxide (DMSO) as an antidote to cisplatin-induced damage to cultured human thyrocytes. The effects of DMSO were studied on human thyroid cells cultured in monolayers and in follicles. Addition of 2% DMSO suppressed the cisplatin-induced decrease in intracellular lactate dehydrogenase, alpha-hydroxybutyryldehydrogenase and creatine kinase activities and in neutral red uptake. DMSO also partially or totally abolished the inhibition of cyclic AMP (cAMP), thyroglobulin (Tg) and triiodothyronine (T(3)) production observed with 7.5, 15 or 30 mum-cisplatin. In the presence of 75 mum-cisplatin, cAMP, Tg and T(3) secretion was always totally inhibited. The increase in thyroxine levels observed with cisplatin administration did not occur in the presence of DMSO. These data indicate that 2% DMSO interacted with cisplatin and therefore prevented the cytotoxic and inhibitory effects of cisplatin on cultured thyroid cells.