An unconventional hypothesis is proposed combining for the first time two different features which are basic for cell metabolism but have been as yet investigated separately: (a) circadian rhythms in enzyme activity, which play a fundamental role in adaptation to the 24h cyclities of environmental cues, and (b) the dynamic character of protein structure which results in continuous shifting between conformational states. Recent data indicate that large time‐scale (hours, circadian) periodicities can thus arise spontaneously in the catalytic characteristics of enzymes in solution, alternating phases of high and low sensitivity to substrate and effectors. The question raises whether conformational oscillators would provide a molecular component of the processes which govern rhythmicity of enzyme activity. This hypothesis also opens a new approach to the study of the temporal organization of enzyme‐enzyme interactions and metabolic channeling, particularly in photoperiodism.