CO2 is required continuously during germination of Streptomyces viridochromogenes spores. Spores incubated in a defined germination medium in the absence of CO2 remain phase bright and do not release spore carbon. In the presence of CO2, the spores initiate germination accompanied by loss of refractility and spore carbon. The CO2 requirement is replaced by oxaloacetate or a mixture of tricarboxylic acid cycle (TCA) intermediates. Labeled CO2 is taken up by germinating spores, and is incorporated into protein and RNA. TCA cycle intermediates and related amino acids contain most of the acid-soluble label following short term exposures of germinating spores to 14CO2. TCA cycle inhibitors repress germination and 14CO2 uptake whereas folic acid antagonists do not. The results indicate that CO2 is incorporated into oxaloacetate which is converted to biosynthetic intermediates required for germination. Operation of the TCA cycle appears to be essential for spore germination. The conclusion is reached that CO2 is required during germination in order to maintain the cycle by an anaplerotic reaction.