SUMMARYSpore, vegetative O and vegetative H agglutinogens were demonstrated as separate entities inBacillusspecies. Spore precipitinogens were distinct from those of the vegetative stage, the latter being associated with the H antigen.Injection of viable spores into rabbits resulted in the formation of antibodies for the vegetative phase as well as spore antibodies, while injection of autoclaved spores gave rise to spore antibodies only.Spore agglutinogens varied in their strain specificity,B. cereusandB. megateriumespecially showing much subspecies specificity, but the spore precipitinogens showed a high degree of species specificity and could be of considerable taxonomic value. The multiplicity of spore precipitinogens in certain species was demonstrated and inter‐species cross reactions were studie