In shake flask growth, the presence of Vitreoscilla hemoglobin (VHb) enhanced production of recombinant alpha-amylase in E. coli by about 80% (generally confirming our previous results). Extension of these studies to growth in oxygen controlled fermenters showed that VHb afforded no advantage in alpha-amylase production when oxygen was not limiting, but resulted in about a 6-fold increase when oxygen was limiting. This increase was due almost entirely to secreted enzyme.