Three Bacillus subtilis genes (termed sspA, sspB, and sspD) which code for small, acid-soluble spore proteins (SASPs) have been cloned, and their complete nucleotide sequence has been determined. The amino acid sequences of the SASPs coded for by these genes are similar to each other and to those of the SASP-1 of B. subtilis (coded for by the sspC gene) and the SASP-A/C family of B. megaterium. The sspA and sspB genes are expressed only in sporulation, in parallel with each other and with the sspC gene. Two regions upstream of the postulated transcription start sites for the sspA and B genes have significant homology with the analogous regions of the sspC gene and the SASP-A/C gene family. Purification of two of the three major B, subtilis SASPs (alpha and beta) and determination of their amino-terminal sequences indicated that the sspA gene codes for SASP-alpha and that the sspB gene codes for SASP-beta. This was confirmed by the introduction of deletion mutations into the cloned sspA and sspB genes and transfer of these deletions into the B. subtilis chromosome with concomitant loss of the wild-type gene.