Prospective trial comparing a combination pH probe-nasogastric tube with aspirated gastric pH in intensive care unit patients. Upper GI bleeding related to stress ulcer syndrome is estimated to affect as much as 15% of patients in an ICU. Since the occurrence of bleeding after ICU admission may be associated with increased morbidity and mortality, many efforts have been directed at defining optimal therapy for stress ulcer prophylaxis. Titration of intragastric pH with antacids or iv doses of H2-receptor antagonists may prevent stress ulcer bleeding in high-risk ICU patients. We evaluated a recently developed pH probe incorporated into an NG tube and compared it with aspiration of gastric contents using pH paper as a means to monitor pH in 22 surgical ICU patients. Regression analysis comparing the intragastric probe pH values with the aspirated pH values showed a good correlation between the two methods (r = .71). This new technique for intragastric pH measurement appears technically simple and clinically applicable for use on patients at risk for stress ulcer bleeding. It may be more accurate than pH paper in patients receiving antacids. 