Dry spores of Streptomyces viridochromogenes exhibited no endogenous metabolism when tested by the sensitive radiorespirometric technique. Wetting the spores resulted in a sharp increase in endogenous respiration followed by a gradual decrease to a constant level, whereby 0.02% of the spore carbon was respired to CO(2) per h. The rate of endogenous metabolism increased slowly as unactivated and heat-activated spores germinated in a defined germination medium, reaching rapid rates only after germination was completed. Components of the defined germination medium, adenosine, l-alanine, and l-glutamic acid, were oxidized to CO(2) at appreciable rates only after germination was complete. The QO(2) (microliters of O(2) uptake per hour per milligram [dry weight] of spores) values for endogenously respiring spores were 3.9 for unactivated and 7.8 for activated spores. Various sugars, amino acids, and organic acids were oxidized only slowly or not at all by unactivated and activated spores. The dry spores contained 5.2 x 10(-2) mumol of ATP per g (dry weight). The ATP content of spores increased approximately 4-fold after suspension in buffer and approximately 11-fold after heat activation. During germination, the ATP level increased to a level of 1 mumol of ATP per g (dry weight) and remained constant. Germination was accompanied by excretion from the spores of approximately 8 and 12% of the total spore carbon from unactivated and activated spores, respectively. A potent germination inhibitor was released from the germinated spores. The germination inhibitor had no effect on heat-activated spores or spores which had begun germination for as short a time as 5 min.