Nine nurses employed in four intensive care units in two hospitals participated in a study to investigate the effects of shift rotation on the circadian electrolyte excretion of sodium and potassium in the urine. Results revealed that the shift rotation followed by these nurses did not produce a significant physiological adaptation to reversing their activity-sleep or their stress patterns. Actually, they continued to follow the same physiological activity patterns whether sleeping during daylight hours or vice versa. The literature of the field is extensively reviewed.