The etiology and pathogenesis of acne arthritis and the arthritis of hidradenitis suppurativa remain unknown. Some patients have an asymmetrical pauciarticular arthritis compatible with the 'reactive' peripheral and central forms of Reiter's syndrome, whereas others have a symmetrical polyarthritis/polyarthralgias syndrome. The cutaneous disease is clinically manifest as acne conglobata or hidradenitis of axilla or groin. We determined human leukocyte antigens (HLA), levels of immunoglobulins, C3, C4 and circulating immune complexes from six patients with acne arthritis. Four of six patients had HLA antigens of B7 Creg group (B7, BW22, B27, BW40, BW42) and all six possessed DRW4. Isolated elevations of immunoglobulins, C3 and C4 were observed. Immune complexes were elevated uniformly. These observations suggest that immunogenetic mechanisms may play a role in the systemic manifestations of these skin diseases.