Purified Escherichia coli RNA polymerase containing the heat shock regulatory protein sigma 32 (gprpoH) was used to inject BALB/c mice, and the spleen cells of an immunized mouse were fused to NS1 cells. Three stable cell lines were isolated which produced monoclonal antibodies to sigma 32. The antibodies varied in their ability to bind sigma 32 which was bound to core polymerase. Each of the antibodies was found to inhibit transcription from the rpoD heat shock promoter to a different extent. Extensive homology at the protein level has been observed between various sigma factors. The monoclonal antibodies to sigma 32 were tested for the ability to cross-react with sigma 70 on Western blots. None of the antibodies reacted with electroblotted sigma 70. The sigma 32 content was examined in total cell extracts during heat shock Levels of sigma 32 were found to increase approximately 4-fold over pre-heat shock levels at five min after temperature upshift. These levels remained slightly elevated above pre-heat shock levels at 10 and 15 min after temperature upshift.