Rhythmometric analysis of a group of phosphohydrolases in mouse liver has been performed along a single 24 hr time scale. The presence of the rhythm was conducted by F test. Statistically significant circadian rhythm was detected in glucose-6-phosphatase (G6Pase) and inorganic pyrophosphatase (InPPase) activity expressed on fresh weight and protein basis. Both G6Pase and InPPase oscillated with a high amplitude of 0.44 U and 1.15 U respectively across the mean value (mesor) of 0.40 +/- 0.42 U and 2.81 +/- 1.14 U per mg protein and with a phase shift of 80 degrees (5.34 hr) among them. On the other hand, alkaline phosphatase (AlPase) did not show any rhythm whereas adenosine triphosphatase (ATPase) showed rhythmic activity on protein basis and oscillated across mesor of 1.84 +/- 0.5 U with an amplitude of 0.52. Acrophase (time for peak activity/mg protein) of G6Pase, InPPase and ATPase was found at 194.2 degrees (13.34 hr), 114.1 degrees (8.0 hr) and at 306.1 degrees (20.4 hr) respectively. AlPase, though did not show significant rhythm, had peak value at 231.8 degrees. Since hepatic G6Pase is a multicomponent and multifunctional enzyme with several overlapping activities (viz. InPPase), coordinated action of G6Pase and InPPase in the regulation of hepatic cell functions has been suggested.