Claims are frequently made that changing from morning to afternoon to night shift at about two- to three-day intervals (rapid rotation) is the best way of organizing 24h staffing. A critical analysis is made of the grounds for these assertion, followed by a review of evidence bearing upon the issue of whether longer periods of rotation are to be preferred. The conclusion is that permanent (zero rotation), fixed-night systems are superior on most counts, and should be implemented for night work, leaving the option of rapid rotation to cover the two (morning and afternoon) day shifts. This said, the multiplicity of shift systems and settings means that this will not always be the method of choice. Furthermore the recommendation should be regarded as provisional pending a search for more data directly comparing the two systems.