The publication of two books on the relationship between dietary restriction and aging has been taken as an opportunity to write a critical review on this field. The content of the two books is summarized and the implications of the major conclusions reached by the authors are appraised. It is concluded that dietary restriction should be more widely studied by gerontologists because of the light it throws on 'clocks' of aging, error detection and repair systems, and the possibilities of devising pharmacological control of these systems.