A variety of radionuclide-labeled, solid foods have been used to measure gastric emptying. Implicit is the idea that the nuclide label identifies the rate of emptying of meal contents. The present studies tested whether different foods empty from the human stomach at different rates. Eight volunteers were fed meals of 200 ml of water + 213 g of beef stew + 52 g of chicken liver, with half the liver as 0.25-mm particles and half as 10-mm chunks, labeled with 99mTc and 113mIn, respectively, or the reverse. Another 8 subjects ingested 200 ml of water + 75 g of noodles, labeled with 123I, + 30 g of liver, labeled with 113mIn. Gastric emptying of each radionuclide was determined for 3 h by measuring the decline of counts in the gastric region of interest, using an Ohio Nuclear S410 gamma camera interfaced to a DEC computer. In each case, appropriate corrections were made for nuclear decay, down-scatter from 113mIn, and septal penetration. Seven of 8 subjects emptied 0.25-mm liver particles more quickly than 10-mm chunks of liver, while 1 subject emptied the two sizes of liver at the same rate. The t 1/2 for the 0.25-mm liver was 70 +/- 10 min; and for the 10-mm liver, 117 +/- 19 min (p less than 0.05). Six of 8 subjects emptied noodles much faster than liver, while 2 emptied the two foods at similar rates. The t 1/2 for the noodles was 52 +/- 8 min; and for the liver, 82 +/- 5 min (p less than 0.02). Since different foods in the same meal were found to empty at different rates, we conclude the gastric emptying of every food in a meal is not accurately represented by the emptying of a single, nuclide-labeled food. The different t 1/2s for the emptying of 10-mm liver in the two meals (p less than 0.05) probably reflected the influence of other meal components on gastric motility.