Our previous studies indicated that Arginine (Arg) plays a key nutritional role in Streptococcus sanguis P4A7 and that this organism can grow on whole casein as the sole nitrogen source. Its protease activities were therefore studied after glucose-limited continuous culture in a chemically-defined medium with either free amino acids or casein as the nitrogen source. Both culture supernatant and cell-associated endopeptidase (EP) and exopeptidase (amino-AP and carboxy-CP) activities were determined. Growth rate (mu) had little effect on EP, 75% of which was consistently in culture supernatants; AP and CP both decreased as mu was increased and both were predominantly cell-associated. At high growth pH, EP was substantially increased while AP and CP activities were optimal at pH 7. The most striking nutritional effect occurred under nitrogen limitation (glucose excess) when EP and AP were greatly increased and CP greatly decreased. It was concluded that S. sanguis is well equipped to scavenge its environment for Arg under a wide range of growth conditions.