Study of the HLA-B grouping of 193 patients with psoriatic arthropathy (PA), compared with that of a control series consisting of 2,706 healthy subjects representative of the French population, revealed a statistically significant link between PA and antigens B27, B17 and B16. In contrast to reported findings of earlier studies, the authors found no link between an HLA-B antigen and any particular topographical or anatomical form of PA. Antigen B27 was not statistically significantly linked with axial forms of PA nor did it protect against peripheral forms. There were neither more cases of peripheral involvement nor less of axial involvement among non-B27 PA patients. The only statistically significant link which could be shown was that between antigen B27 and sacroiliac involvement in recent PA, present for less than 10 years. The authors conclude that in 60 per cent of cases, PA is associated with a particular antigen: B16, B17 or B27. Involvement of the sacroiliac joints is more common in cases of B27 PA and above all occurs earlier than in others. Regardless of its HLA group, PA as it progresses shows an increasingly clear mixture of spinal, peripheral and sacroiliac lesions, which forms the basis of the originality of this condition.