Capnocytophaga gingivalis was grown with proteins (albumin, collagen, mucin and hemoglobin) as carbon and energy sources in chemostat culture. The μmax (0.34 h−1) and biomass yield (0.96 g · l−1) were as high with hemoglobin (3 g · l−1) as with glucose (3 g · l−1) (20). Albumin, collagen and mucin also supported an increased μmax, or yield or both, in comparison with basal (tryptone/thiamine) medium. In steady-state, trypsin-like protease specific activity increased 3- to 5-fold in the presence of albumin, collagen and hemoglobin; whereas the greatest increase (21-fold) in α-glucoside activity was in the presence of mucin. There were significant, but less substantial changes in other hydrolytic enzymes (aminopeptidase, acid and alkaline phosphatases). The bulk of the detected hydrolytic activity (>66%) was associated with the cells. The data indicate that C. gingivalis regulates its production of hydrolytic enzymes in response to environmental conditions.