Dehiscence of Actinoplanes sp. 7-10 sporangia is triggered by wetting of the spores. This process requires time because of the hydrophobic nature of the sporangial envelope; it can be speeded up and enhanced by a wetting agent. Once wetted, the spores swell, usually ripping the sporangial wall, and escape as motile elements when functional flagella are synthesized. Flagellation and motility are separate phenomena, both of which lose intensity with age. Spores from old sporangia can regain motility when supplied with an exogenous carbon source, but, when provided only with water, phosphate buffer, or amino acids, flagellation takes place without motility. Deflagellation-reflagellation experiments indicated that functional flagella can be reformed only in presence of both amino acids and glucose which must be added within 180 min of deflagellation. Inoperative flagella were formed in the presence of inhibitors of nucleic acid synthesis, such as 6-azauracil, but inhibitors of protein synthesis, such as chloramphenicol, did not interfere with reflagellation. Flagellated spores remained so after germination.