This study examined the effects of motion sickness and antimotion sickness drugs on gastric emptying (GE). Drugs were tested in normal and motion sick subjects. To induce motion sickness, subjects performed head movements while seated in a rotating chair. Gastric emptying of liquid (300 mL) was determined by nuclear medicine techniques, whereas gastric electrical activity, the electrogastrogram (EGG), was monitored from surface (cutaneous) electrodes positioned over the abdominal area. Gastric emptying was severely inhibited at the peak of motion sickness symptoms, but returned to normal 15 minutes later when symptoms abated. In normal (non-motion sick) subjects intramuscular (IM) scopolamine (0.1 mg) and IM promethazine (25 mg) inhibited GE, whereas erythromycin ethylsuccinate (EES) suspension (200 mg) given orally increased GE. When administered to motion sick subjects, IM scopolamine and IM promethazine added slightly, but not significantly, to the inhibition of GE already present. Oral EES did not significantly alter GE in motion sick subjects. Although EGG frequency remained within normal limits (approximately 2.5-3.5 cpm) after liquid ingestion in both normal and motion sick subjects, EGG amplitude was differentially affected in the two groups. Electrogastrogram amplitude increased twofold to fourfold after liquid ingestion in normal, but not in motion sick subjects. The results suggest that (1) maximal inhibition of GE is coincident with peak motion sickness symptoms, (2) both IM scopolamine and IM promethazine inhibit GE in normal subjects, but do not add significantly to the inhibition of GE already established during motion sickness, (3) orally administered erythromycin enhances GE in normal, but not in motion sickness subjects, and (4) the normal stimulatory effect of liquid ingestion on gastric motility does not occur in motion sick subjects.(ABSTRACT TRUNCATED AT 250 WORDS)