The dipeptide antibiotic bacilysin, when added externally to the early exponential-phase cultures, markedly limited its own synthesis. It was shown in cell-free extracts that the feedback effect does not involve the inhibition of bacilysin synthetase, the enzyme catalyzing bacilysin formation. We also studied pH and temperature dependence of bacilysin production. Production was highest at about pH 6.8 and at 25 degrees C.