The objective of this study was to determine the difference between gastric residual volume measurements without giving air compared to giving 30 ml of air via the feeding tube. This experimental study was on 60 subjects fed enterally at a university hospital. Data collection was with the 12-item "Gastric Residual Volume Measurement Instructions" and "Gastric Residual Volume Observation Form." The same subjects composed experimental and control groups. Gastric residual volume measurements were taken before feedings at 10:00 a.m., 1:00 p.m., and 4:00 p.m. with a 60-ml syringe. First measurement was taken without giving air by withdrawing the syringe piston at 2-3 ml/second. Second measurement was applied by giving 30 ml of air and withdrawing the piston at the same speed. Student's t test was used for data analysis. A total of 180 measurements were made for each method. Gastric residual volume averages were 3.71 +/- 7.97 ml without air and 3.78 +/- 8.08 ml with air. The difference between averages was statistically significant (p < .05). Difficulties withdrawing the syringe piston without giving air occurred in 85% of the intermittently enterally fed patients and 22.8% of those fed continuously. Gastric residual volume measurements with air were higher than those without air. The aspiration procedure with air was easier. Gastric residual volume measurements should be made with 30 ml of air and by withdrawing the syringe piston at 2-3 ml/minute.