Geometric-mean correction of gastric radioactivity can be used to correct for the distribution, depth, and attenuation of the radionuclide. Anterior image counts were compared with the geometric mean of anterior and posterior counts, using a computer-assisted gamma camera. Phantom and human studies using Tc-99m and In-111 were used to evaluate the difference between anterior-only and geometric-mean data. The effect of meal size on gastric emptying was studied using Tc-99m and In-111 simultaneously as solid-phase and liquid-phase markers. Differences between the anterior data and AP-PA data corrected by geometic mean were compared in ten healthy male subjects. The average half-emptying times for solid food, with 1692-, 900-, and 300-g meals, were 277, 146, and 77 min, respectively. Average half-emptying times for liquid were 178, 81, and 38 min for the same meals.