Objective: Since peritoneal dialysis causes peritoneal fibrosis, we examined how glucose (osmotic factor), mannitol (osmotic control), and angiotensin II (AngII) regulate proinflammatory cyclooxygenase 2 (COX-2) in primary rat peritoneal mesothelial cells. Materials and Methods: For this study, we used the following material (n = 4-8 cell lines): cells, passages 1-2; 125I-AngII receptor surface binding (AT1R antagonist losartan, AT2R antagonist PD123319; both 10 µM); intracellular calcium probe calcium-5; COX-2 immunoblotting (ß-actin normalized); real-time PCR of COX-2 gene PTGS2, and NF-κB inhibitor Ro-1069920 (5 µM). Results: AngII surface receptors were predominantly AT1R (minimally AT2R). AngII and glucose increased COX-2 protein expression concentration dependently; mannitol also increased COX-2 expression. Maximal COX-2 protein expression was observed after 6 h (AngII) and 24 h (glucose, mannitol). The time course of increases in PTGS2 mRNA levels reflected that of COX-2 protein expression. At optimal exposure conditions (time/concentration), glucose was 5-fold more efficacious in stimulating COX-2 protein expression than AngII or mannitol. Losartan fully inhibited COX-2 protein responses to AngII and mannitol, but minimally inhibited responses to glucose. Ro-1069920 fully inhibited COX-2 protein responses to each effector. Conclusion: AngII, glucose, and osmotic stress (mannitol) activate COX-2; NF-κB may be an ideal site for COX-2 blockade, and COX-2 activation by osmotic stress requires AT1R, but activation by glucose is more robust and mechanistically complex.