Since 1981, all pregnant women presenting to our department with a pruritic dermatosis have been investigated by histological and immunopathological techniques. We recruited 111 patients and performed skin histology in 77, 109 direct immunofluorescence tests (DIF), 74 indirect immunofluorescence tests (IIF) and 15 Western blots (WB). We identified: (i) five typical cases of pemphigoid gestationis (PG) (4.5%), corresponding to an incidence of 1/7000 pregnancies. (ii) Five cases without PG but showing circulating anti-BMZ antibodies of IgM type. With the exception of one case, clinical features were homogeneous--occurrence of erythematous papular and/or urticarial lesions on the trunk, and less often, on the limbs between the 32nd and 38th week of pregnancy. Rapid clearance of lesions within a few days was the rule. Whenever performed, DIF was negative and IIF showed circulating anti-BMZ antibodies of IgM type. Western blot studies were negative in these five cases. (iii) One hundred and one cases with negative immunofluorescence tests, considered to be suffering from polymorphic eruption of pregnancy. Our results show the value of systematic immunopathological investigations in pregnant women presenting with a pruritic dermatosis, and raise the possibility of a new entity, as defined by circulating anti-BMZ antibodies of IgM type.