SUMMARY Bacteroides amylophilus strain H I 8 produced protease(s), active at pH 7.0, when grown anaerobically in a simple maltose, ammonium sulphate, cysteine, sodium bicarbonate and salts medium. Protease production was neither induced nor repressed by a wide range of nutrients. Protease was synthesized by exponentially growing organisms and 20% of it was liberated into the growth medium. The cell-bound protease was completely accessible to the protein substrate. Protease production was proportional to ammonium sul- phate and maltose concentration in the ranges in which these nutrients were growth limiting.