Twenty-four antigens of Bartonella bacilliformis, a bacterium which causes bartonellosis in residents of high altitude valleys of the Andes, were identified by immunoblot and immunoprecipitation using rabbit anti-Bartonella sera as well as sera of patients. The antigens were designated according to their relative molecular mass which ranged from 16 to 160 kDa. Twelve antigens were detected by antibodies in sera of bartonellosis patients using immunoblot, of which six antigens were detected by immunoprecipitation. Antigens 25, 46, 65, 75, 99, and 160 were identified ad probable cell wall antigens. Antigens 50, 65, and 75 detected long-persisting antibodies. Crude Bartonella antigen applied to ELISA reacted with anti-Chlamydia psittaci antibody as well as with antibody of unknown identity in human sera, whereas immunoblot and immunoprecipitation with Triton soluble antigens revealed Bartonella-specific results. Seven Bartonella antigens were prepared by high performance liquid chromatography of which one antigen (48 kDa) reacted Bartonella-specific when applied to ELISA. It was concluded that specificity of antibody determination with crude Bartonella antigen should be confirmed by either immunoblot or immunoprecipitation.