The antigenic relationship between two species of Leishmania (L. mexicana amazonensis and L. braziliensis braziliensis) was analysed using crossed-immunoelectrophoresis with an intermediate gel. Rabbit hyperimmune sera were prepared by subcutaneous inoculations of soluble antigens obtained from each species, emulsified in Freund's adjuvant. The antisera were then tested by immunodiffusion and electrophoresis; soluble antigens obtained from promastigote forms were submitted to ultrasonication and ultracentrifugation. Immunoelectrophoresis with homologous and heterologous antisera demonstrated the existence of some antigens which were species specific and some which were common to both species. The importance of these antigens is discussed.