Production of a lipopeptide surfactant, surfactin, by Bacillus subtilis ATCC 21332 was highly enhanced when iron concentration in the medium was raised from 4 mu M to the few mM level. This iron enrichment of the medium also resulted in increased biomass concentration. With 1.7 mM iron sulfate added to the media of different initial iron concentrations or at different stages of growth, surfactin concentration can be raised to levels of several hundred mg l(-1) in general. Acidification of the broth was usually observed following the iron addition, and surfactin in the broth disappeared rapidly dire to precipitate as soon as the pH level dropped below 5.0; however; if this acidification phenomenon was delayed, avoided Vbr reasons still unknown), or reversed (bp alkaline addition), surfactin production was highly enhanced to as high as 3,500 mg l(-1) which was almost ten times over the previously reported level for this strain and higher than most reported values for genetically improved strains.