Effects of pH on beta-galactosidase expression and stabilization were investigated using recombinant E. coil harboring an expression vector with a thermally-inducible P(L)promoter. Expression of beta-galactosidase was strongly promoted by lowering culture pH when culture temperature was raised to the induction temperature. Optimal pH for induction ranged from 5.4-5.8. The degradation of expressed beta-galactosidase could be reduced by lowering the culture temperature while at the same time slightly increasing the culture pH in the beta-gal degradation stage.