Kinetin (100 mu M) markedly accelerated the degradation rate of lipids and proteins in cotyledons excised from germinated seeds and maintained in darkness. Protein decomposition was accompanied by an increase in proteolytic activity, which was much higher in kinetin-treated cotyledons. Analysis of protein patterns revealed 6 significant polypeptide fractions. During 96 h of incubation, 3 fractions of low molecular weight disappeared whereas heavier proteins remained almost at the same level. The degradation of all 6 fractions was strongly accelerated by kinetin. It is suggested that cytokinins may be considered as the main factors regulating the rate of reserve mobilization during the early developmental stages.