Western blot analysis of sera from 32 patients with acute clinical leishmaniasis due to Leishmania infantum showed the simultaneous presence of antibodies against 4 antigens with molecular masses of 18, 21, 23, 31 kDa. The simultaneous presence of these 4 antigens was specific to the clinical disease and it was not detected in 47 sera from asymptomatic individuals living in the leishmaniasis endemic area of Alpes-Maritimes (southern France) or in 37 sera from patients with other protozoan infections.