Daunorubicin and its derivative doxorubicin are antitumour anthracycline antibiotics produced by Streptomyces peucetius. In this study we report isolation of stable mutants of S. peucetius blocked in different steps of the daunorubicin biosynthesis pathway. Mutants were screened on the basis of colony colour since producer strains are distinctively coloured on agar plates. Different mutants showed accumulation of aklaviketone, epsilon-rhodomycinone, maggiemycin or 13-dihydrocarminomycin in their culture filtrates. These results indicate that the mutations in these isolates affect steps catalysed by dnrE (mutants SPAK and SPMAG), dnrS (SPFS and SPRHO) and doxA (SPDHC) gene products.