Secondary metabolite production by Streptomyces is often highly sensitive to oxygen supply, which can be limiting in large-scale fermentations. In an attempt to improve oxygen utilization by the cells, we expressed a heterologous bacterial hemoglobin gene in Streptomyces coelicolor and Streptomyces lividans. Hemoglobin expression was demonstrated by immunoblot analysis and carbon monoxide binding activity. In batch fermentations run under reduced aeration, the expression of hemoglobin in S. coelicolor resulted in a ten-fold increase in specific yields of the aromatic polyketide, actinorhodin. Actinorhodin yields were also much less sensitive to aeration conditions in the hemoglobin-expressing strain. In addition, hemoglobin-expressing S. lividans cells grown under reduced aeration had higher final cell densities and exhibited greater oxygen consumption rates than non-expressing cells.