Continuous fermentations were performed in order to correlate the production of retamycin, an anthracycline antibiotic produced by Streptomyces olindensis in submerged cultures, with the dilution rate. Maximum retamycin production was achieved at a dilution rate of 0.05 h(-1) (D = mu(x) = 0.05 h(-1)), while higher dilution rates caused a decrease in antibiotic production, which ceased completely at a dilution rate of 0.30 h(-1). Otherwise, biomass productivity was favoured by high dilution rates, achieving a maximum at D = 0.25 h(-1), whereas retamycin productivity reached a maximum at D = 0.05 h(-1). Dilution rate influenced morphology, which was assessed by image analysis. The percentage of clumps decreased with an increase in dilution rate, with a correspondent increase in pellet percentage. (C) 2003 Elsevier Ltd. All rights reserved.