An electrophoretically homogenous aggregate of acid trehalase, invertase and an unidentified 37-41 kDa protein was purified from Saccharomyces cerevisiae. N-terminal analysis of the protein revealed an amino acid sequence identical to that of Bgl2p (endo-beta-l,3-glucanase) of S. cerevisiae. Acid trehalase activity with co-eluted glucanase activity was observed from late growth phase through early stationary phase. Pools with high percentage of Bgl2p corresponded with high acid trehalase activity. A BGL2 deletion strain had lower acid trehalase activity. The 37-41 kDa protein represents Bgl2p which, besides imparting glucanase activity, could also be acting as a regulator for the acid trehalase activity by association in the enzyme aggregate.