The immunoprotective behaviour of the 30-kDa secretory glycoprotein of Mycobacterium tuberculosis H37Rv has been investigated in different adjuvant systems in two mouse strains, NMR1 and C57BL/6J. In comparison with Freund's incomplete adjuvant (FIA) and dimethyldioctadecyl ammonium bromide (DDA), the 30-kDa glycoprotein complexed with polylactide-co-glycolide microparticles (PLG-MPs) induced maximum immunoreactivity in the two mouse strains. As compared with controls, immunisation with 30-kDa-PLG-MPs resulted in significantly greater protection in animals challenged with 1 x LD50 of M. tuberculosis H37Rv on the basis of survival rates and number of cfu in the infected organs 30 days after challenge. The degree of protection provided by 30-kDa-PLG-MPs was similar to that obtained with 30-kDa-FIA and higher than BCG immunisation. These findings suggest that biodegradable PLG microparticles can be used as an efficient carrier system for the key immunoprotective 30-kDa secretory protein antigen of M. tuberculosis H37Rv.