Tiopronin (50 mg/kg) and D-penicillamine (50 mg/kg) do not exhibit anti-inflammatory effects in classic animal models (carragenin oedema, granuloma cotton pellets) but suppress pertussis vaccine oedema, an immunological model, when given with a long-lasting dosing regime. Tiopronin and D-penicillamine also fail to inhibit PG release by phagocytosing leucocytes when the concentrations used were in the same range as human blood levels (5-15 micrograms/ml). Indomethacin (1, 3 and 5 mg/kg) instead significantly inhibits both the in vivo and in vitro models considered. This may imply a different mode of action of both tiopronin and D-penicillamine from indomethacin. Tiopronin also possesses similar effects to D-penicillamine suggesting that their overall anti-rheumatic action may have common elements.