An enzyme-linked immunosorbent-assay (ELISA) for the detection of antibodies against Thermoactinomyces sacchari associated with bagassosis has been described and compared with the counter-immunoelectrophoresis (CIE) assay in forty-five bagasse workers; twenty-six of whom had symptoms consistent with bagassosis, and ten who were normal blood-bank donors. The ELISA was more sensitive than CIE in detecting antibodies against the double dialysis antigen used. There was a significantly (P < 0.05) greater number of ELISA-positive individuals (82%) than those who were precipitin positive (60%). Results of the ELISA also gave a significantly better correlation (P < 0.05) with the clinical diagnosis (88%) than did the precipitin test results (58%). The ELISA was useful in quantitating antibodies in the sera. The symptomatic group of bagasse workers did not have significantly higher titres in the ELISA than the group of exposed but asymptomatic subjects. We conclude that the ELISA is a sensitive and specific test, which is readily available and widely applicable for the detection of immunization in bagasse workers.