Six geographically distinct isolates of Leishmania amazonensis causing diffuse cutaneous leishmaniasis (DCL) (from Bahia and Maranhão, in Brazil and Guarico, in Venezuela) were characterized by immunoblot analysis to see whether any geographical or strain-related differences existed in antigenic composition. Western blots of promastigote homogenates were reacted with polyclonal sera from patients infected with L. amazonensis with the various forms of clinical disease. The pattern of antigenic reactivity of these strains revealed the presence of shared antigenic components between geographically distinct L. amazonensis isolates causing DCL, when tested with the sera of the infected patients. In certain cases, however, some polyclonal sera also detected antigenic fractions unique to the strains examined. Variation was observed between the antigenic components of some isolates of L. amazonensis that were recognized by a single serum, and between the antigenic components of a single isolate of L. amazonensis that were recognized by the different patients' sera. However, no constant association was found between the antigenic components identified in these isolates and the geographical area of isolation. These results indicate that, although these parasites appear to be closely related antigenically, they also possess some strain-related antigenic differences.