Fifty-two patients with psoriatic arthritis (PA), treated with auranofin (AF), were entered into a one year prospective, open study. The total group showed a significant increase in frequency of HLA antigens A1 and B38, and a reduction of B5 when compared to healthy controls. There was a remission or an important improvement of disease in the 51% of 45 patients who completed the study. The rate of withdrawal due to side effects was low (8.8%) and the toxicity was mild in nature (diarrhoea and mucocutaneous rash). We prospectively sought predictors of response using HLA antigens, and clinical and laboratory parameters at the beginning of therapy. The only 3 factors found to be related to outcome were duration of psoriasis, physician and patient assessment of disease activity. No laboratory data or HLA specificities could be associated with substantial response to AF therapy.