BACKGROUND: It has been known that alveolar macrophage exposed to bacterial lipopolysaccharide (LPS) induces a lots of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) mRNA expression. The Authors elucidated the effects of iNOS mRNA expression by inhalational anesthetics (isoflurane) on endotoxemic rats and positive pressure ventilation with and without LPS. METHODS: Fifty Sprague-Dawley rats (250 - 270 g) were anesthesized with urethane injected in the peritoneal cavity. Then the expression of iNOS mRNA in the alveolar macrophages of the rats were measured after injection of LPS, 2 hours of isoflurane (0.5 - 2.5%) anesthesia, and 2 hours of positive pressure ventilation. The activities of iNOS in macrophages were measured by analysing iNOS mRNA expression by Northern blot analysis with autoradiography using the polymerase chain reaction (PCR) method. RESULTS: The size and patterns of the iNOS mRNA band in the 0.5 - 2% isoflurane group were almost same as with the control group. The size of the iNOS mRNA band in the 2.5% isoflurane group increased more than in the control group. In the continous positive-pressure ventilation with LPS group, the iNOS mRNA band was slightly increased compared to the normal lung and the continous positive-pressure ventilation without LPS group. CONCLUSIONS: Higher concentrations of isoflurane anesthesia may evoke the expression of iNOS mRNA in a septic model. Positive pressure ventilation in sepsis may induce iNOS mRNA production.