We investigated the influence of the pituitary gland on the circadian organization of the urinary rhythms of sodium, potassium, phosphate and water. Control and hypophysectomized (HPX) rats were studied during a light‐dark (LD) (12h:12h) cycle, constant illumination (LL) and constant darkness (DD). The latter was achieved by bilateral ocular enucleation. In addition to anterior pituitary insufficiency some rats exhibited partial diabetes insipidus (HPX‐DI) and some did not (HPX‐NDI). During DD the mean period was 24.5 hrs for control rats and HPX‐NDI rats. In contrast to blind rats animals maintained under LL conditions showed a decrease in period after 8 days, i.e. from about 25.3 hrs to about 24.4 hrs in all groups. Generally, no significant differences in period were found between HPX‐DI, HPX‐NDI and control rats. Under LD conditions the acrophases for sodium, potassium and water excretion shifted, occuring about 6 hrs later in HPX‐NDI rats and about 9 hrs later in HPX‐DI rats compared to control animals. In contrast, the acrophases for phosphate remained unchanged for HPX rats. Normal phase angles were restored by corticosterone and thyroxine substitution. This study demonstrates that the pituitary gland is not essential for the generation of urinary excretory rhythms; however, this organ plays a critical role in the phase setting of some renal excretory rhythms.