We compared the propensity of several strains of guinea pigs to develop autoimmune experimental uveitis and autoimmunity following immunization with retinal-uveal antigens in complete Freund's adjuvant. The Hartley and NIH strains developed the disease more frequently and more severely than the strain 13 animals. The strain 2 guinea pigs did not develop the disease at all. In addition, the strain 2 did not make as much delayed hypersensitivity or as much antibody as the Hartley and NIH strain animals. NIH guinea pigs lacking the fourth component of complement made as much disease as those with that enzyme.