Mycobacterium habana (M. simiae serovar-1) is a candidate vaccine for mycobacterial infections on the basis of the protection shown by this strain. We prepared 3 fractions of M. habana, i.e. the cell wall (CW), the cell membrane (CM) and the cytosol (CS). Protein antigens of these fractions were resolved by SDS-PAGE and subsequently probed with the sera of leprosy and tuberculosis patients and also antiBCG antibodies. We saw 3 major protein bands at congruent to 33 kD in the CW, congruent to 38 kD in the CM and congruent to 22 kD in the cytosol (CS) after coomassie blue staining of the gels. Pool leprosy patients' serum had identified proteins of congruent to 26 kD in CW, congruent to 35 and congruent to 18 kD in CM and congruent to 24 kD in the CS which have not been seen by the TB patient's serum pool. Pool serum of tuberculosis patients has identified 1 protein at congruent to 10 kD in the CW and a broad band between 20 and 24 kD and 1 at congruent to 4 kD in the CM which have not been visualized in the pool leprosy patient's serum lane. The proteins of M. habana which are recognized only by leprosy antisera or only by tuberculosis antisera could be exploited for developing diagnostic agents against these infections.