Production of a mutant of the enzyme alpha-lytic protease from recombinant E. coli JM109 increased from 50 units/l to 750 units/l as the dissolved oxygen was decreased from above 30% saturation to near zero during batch growth on a complex medium. This represents a 60-fold increase in specific protease production (units/g cell dry wt.). Limiting the oxygen supply decreased the maximum growth rate from 0.55 h(-1) to 0.066 h(-1) which may in turn regulate the synthesis of recombinant protease in this system so that increased levels of product are obtained.