The regulation of the ssb gene of E. coli has been studied. We reported earlier that the SOS box of the neighbouring uvrA gene also controls the transcription of the ssb gene. Detailed analysis of the upstream region of ssb by S1 mapping reveals the existence of three in vivo functional promoters of which the most upstream one (PI) is inducible by DNA damage. Measurement of galactokinase synthesis using galK fusion plasmids indicates that the uninduced level of transcription from the PI promoter is low. Ssb multicopy plasmids lacking the PI promoter still complement the UV sensitivity of an Ssb mutant. The role of the three promoters in the regulation of the level of Ssb protein in the cell, is discussed.