Fasciola gigantica cathepsin-L cysteine proteinase and recombinant cathepsin L 1-D were assessed for their potential in the immuno-diagnosis of F. gigantica infection in buffaloes. A diagnostic ELISA, based on these two antigens, was developed to detect antibodies against F. gigantica in water buffaloes. Sensitivity of the ELISA was assessed using sera from buffaloes experimentally or naturally infected with F. gigantica from F. gigantica endemic areas and its specificity by probing the sera of the host from F. gigantica non-endemic area. Our earlier studies under experimental setting showed 100% sensitivity of cathepsin-L ELISA in the diagnosis of fasciolosis in buffaloes, with the earliest detection of infection at 4 weeks post-infection. However, under field situation of natural F. gigantica infection, this sensitivity declined to 97.1% but specificity of the test remained 100%. Cross-reactivity of the antigen was checked with Schistosoma indicum, S. spindale, Paramphistomum epiclitum, Gastrothylax spp., Gigantocotyle explanatum, hydatid and Strongyloides papilossus in the bubaline host, naturally infected with these helminths. F. gigantica cathepsin-L and the recombinant cathepsin L-1D does not cross-react with these helminth parasites in natural mono or mixed infection of the host. The present ELISA contributes a relatively sensitive and reliable tool for the early serodiagnosis of bubaline fasciolosis.