Male rats, IOPS OFA strains, were injected s.c. with doses of lead acetate (0.5 to 30 mg Pb2+/kg/day) and nickel chloride (0.05 to 5 mg Ni2+/kg/day), for 3 days prior to being challenged for immediate hypersensitivity induced by ovalbumin/antiovalbumin system. The vascular permeability was statistically increased in animals of each group (P less than 0.001, Student's t-test). These results may indicate an action of lead and nickel salts on mast cells and their membranes, but also an action on the vasodilation induced by vasoactive amines.