Sephadex G100 chromatography and preparative sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using 16% polyacrylamide gels were used for the partial purification of 16-18 kDa proteins able to stimulate Salmonella enteritidis 11RX-primed T cells of (BALB/c x C57BL/6J)F1 mice. A soluble antigen (Ag) extract of S. enteritidis 11RX (s11RX) was used as the starting material for purification for two reasons. First, s11RX had been previously shown to induce in vitro proliferation of Salmonella-primed T cells; second, initial analysis of SDS-PAGE fractionated s11RX Ag using the 'T cell western blot' technique indicated that T cell stimulatory activity was located only in the 16-18 kDa region. The partially purified antigens were able to elicit delayed-type hypersensitivity reactions in vivo, and stimulated in vitro proliferation and interleukin-2 release from 11RX-primed T cells and T cell lines and clones derived from these cells, indicating that they are major antigenic determinants of S. enteritidis 11RX. Testing of 16-18 kDa proteins of several other bacteria indicated that these antigens may be 'common' and expressed by a number of organisms belonging to the Enterobacteriaceae.