Serial pH measurements were performed on 366 gastric aspirates from 20 critically ill patients receiving nasoenteral feeding with Osmolite or Isocal HCN, with no other means of gastric acid buffering. Ten patients (group A) received continuous intraduodenal feeding, and ten patients (group B) received continuous intragastric feeding. Gastric pH was at least 5.0 in 33 (23%) aspirates from group A, compared to 120 (54%) from group B (p < .001). Only two (20%) group A patients had gastric pH values of 5.0 or greater for at least half of the measurements, compared to six (60%) group B patients. These data indicate that continuous intragastric feeding with Osmolite or Isocal HCN controlled gastric pH better than did intraduodenal feeding. However, neither technique adequately neutralized gastric acidity in these critically ill patients.