Bee venom, administered subcutaneously, suppressed the development of carrageenan-induced paw edema and adjuvant arthritis in the rat in a dose-related manner. A single dose of bee venom administered subcutaneously the day before or on the day of injection of complete Freund's adjuvant (CFA) effectively suppressed the development of polyarthritis. This suppressive effect decreased progressively as dosing was delayed. Bee venom was found to be most effective when mixed and injected (sub-plantar) together with CFA, the disease-inducing agent. Similarly, antigens such as egg albumin, when incorporated into CFA, and injected into the hind paw, prevented the development of arthritis. These results suggest that at least two mechanisms are involved in the anti-arthritic action of bee venom: (1) alteration of the immune response, probably via antigen competition, and (2) an anti-inflammatory action via corticosteroids or through an as yet undetermined mechanism.