Using Streptomyces coelicolor microarrays to discover regulators of gene expression in other Streptomyces species, we identified wblA, a whiB-like gene encoding a putative transcription factor, as a down-regulator of doxorubicin biosynthesis in Streptomyces peucetius. Further analysis revealed that wblA functions pleiotropically to control antibiotic production and morphological differentiation in streptomycetes. Our results reveal a novel biological role for wblA and show the utility of interspecies microarray analysis for the investigation of streptomycete gene expression.