['Circadian rhythms in mammals depend upon the cyclic oscillations of transcriptional/translational feedback loops in pacemaker cells of the suprachiasmatic nucleus. The rise and fall of clock-related proteins is a function of synthesis and degradation, the latter involving phosphorylation by casein kinase Iepsilon and delta.', 'Earlier studies by our lab described the actions of a selective CKIepsilon/delta inhibitor, PF-670462, on circadian behavior in rats; the present work extended these studies to a diurnal species, Cynomolgus monkeys.', 'General cage activity was used to estimate the circadian rhythms of eight telemeterized monkeys under baseline conditions and following s.c. doses of PF-670462.'] Do inhibition of casein kinase I epsilon/delta produces phase shifts in the circadian rhythms of Cynomolgus monkeys?