A micro capsule agglutination test (MCAT) was evaluated for its usefulness in the diagnosis of leptospirosis. The test was performed on 180 serum samples from 120 patients suspected to have leptospirosis and the results were compared with those obtained by microscopic agglutination test (MAT). The overall sensitivity and specificity of the test in comparison with MAT were 84.7 and 87.0 per cent respectively. Further, to study the relative merits of MCAT and MAT in diagnosing leptospirosis early in the course of the disease, its sensitivity and specificity during the early stages of the disease were compared with those of a single MAT done on acute samples in 60 patients from whom paired samples were available. The test appeared to have a higher sensitivity than MAT during the early stages of the disease (75% vs 58.3%) though the specificity was less than that of MAT (83.3% vs 100%). The sensitivity of the test declined to 61 per cent three to four weeks after the onset of illness. MCAT detected antibodies against serogroups Australis (76.9%), Autumnalis (100%) Ballum (100%), Canicola (100%), Cynopteri (100%), Grippotyphosa (71.8%), Icterohaemorrhagiae (93.3%), Javanica (100%), Pomona (75%) and Pyrogenes (100%). MCAT appears to be a useful screening test for early diagnosis of leptospirosis. It is a simple and easy to read test which does not require any special expertise or equipment.