Protein synthesis in response to heat shock was induced in the proliferative and secretory human endometrium as well as in human decidua during a 2-h incubation period at 41 degrees C. A major 70 K stress protein and two minor stress proteins of 88 and 94 K were detected after [35S]methionine incorporation followed by SDS polyacrylamide gel electrophoretic separation and autoradiography of dried gels. Two dimensional isoelectric focusing followed by fluorography showed the major 70 K stress protein to consist of at least six polypeptides of pH 4.6 to 5.5, the 88 K to consist of at least four polypeptides, of pH 5.5 to 6.0, and the 94 K to consist of at least three polypeptides of pH 4.6 to 5.2. Stress proteins in the human endometrium and decidua may prove to be of physiological significance in reproductive events.