Changes in the expression of endothelial nitric oxide synthase (eNOS) in the peritoneum could be involved in the peritoneal dysfunction associated with peritoneal inflammation. Demonstrated recently in bovine endothelial cells was the existence of cytosolic proteins that bind to the 39-untranslated region (39-UTR) of eNOS mRNA and could be implicated in eNOS mRNA stabilization. The present work demonstrates that eNOS protein is expressed in human endothelial and mesothelial peritoneal cells. Escherichia coli lipopolysaccharide shortened the half-life of eNOS message, reducing eNOS protein expression in peritoneal mesothelial and endothelial cells. Moreover, under basal conditions, human peritoneal samples expressed cytosolic proteins that bind to the 39-UTR of eNOS mRNA. The cytosolic proteins that directly bind to 39-UTR were identified as a 60-kD protein. After incubation of human peritoneal samples with lipopolysaccharide, the binding activity of the cytosolic 60-kD protein increased in a timedependent manner. Studies are now necessary to determine the involvement of this 60-kD protein in the regulation of eNOS expression in peritoneal cells and particularly its involvement in the peritoneal dysfunction associated with inflammatory reactions.