As demonstrated in the preceding paper, normal bile has a significant inhibitory effect on aacterial [beta]-glucuronidase which is known to play an iirportant role in the development of calcium bilirubin-ate stones. To elucidate the phenomenon, a number of substances that are generally accepted as bile constituents were independently examined for the effect on the activity of bacterial [beta]-glucuronidase. It was then revealed that fatty acids, lecithin, cholesterol and inorganic ions except Cu++ did not influence the enzyme activity. Bile acids inhibited the activity of a commercial preparation of this enzyme but rather activated bacterial [beta]-glucuronidase of infected bile. Free bilirubin as well as glucuronic acid exhibited a considerable inhibitory power only at a concentration exceeding the actual concentration in normal oile. Cu++ inhibited the enzyme activity at a concentration near the normal Cu content of bile, but there was no significant correlation between the Cu content and the inhibitory power of normal bile specimens. The results thus seem to suggest that bile includes a strong inhibitor of this enzyme which has not yet been identified as a normal constituent of bile.