Streptomyces coelicolor was found to produce a third secondary metabolite, in addition to the antibiotics methylenomycin A and actinorhodin previously described. This is a red pigmented, highly non-polar compound with antibiotic activity against certain Gram-positive bacteria. Mutants lacking the red compound fell into five cosynthetic classes. Representatives of each of the five classes were mapped to the chromosome of the producing organism, in a closely linked cluster. Genetic studies provided evidence that this new metabolite is distinct from actinorhodin and indicated that the two pigments do not share parts of the same biosynthetic pathway.