<jats:p> <jats:italic>Streptomyces lactamdurans</jats:italic> , producer of the antibiotic cephamycin C, excretes at least two proteases. Physiological studies indicate that antibiotic synthesis and serine protease formation are coordinately regulated. Both are produced only after culture growth ends, and they appear with essentially identical kinetics. In addition, strains which produce superior levels of cephamycin C form equally superior levels of the serine protease. Genetic evidence reveals that the syntheses of the antibiotic and serine proteases are associated with sporulation. Mutants which fail to produce aerial hyphae (bald mutants) also fail to synthesize the antibiotic and serine proteases.