Ondansetron is a competitive serotonin 5-HT3 receptor blocker that has proved useful in the prevention of emesis due to cisplatin and other cancer chemotherapeutic agents. In a randomized, open-label, crossover study in 24 healthy male subjects, the relative bioavailability of a single 8-mg tablet was compared with that of an 8-mg solution using the two one-sided t-tests. The tablet and solution formulations were bioequivalent, as confirmed by similarities in mean Cmax (26.3 vs 27.7 ng/mL), Tmax (1.79 vs 1.70 h), and AUC (166.0 vs 167.3 ng.h/mL) values. In another randomized, open-label, crossover study in 12 healthy male subjects, the bioavailability of an 8-mg ondansetron tablet administered 5 min after a standard meal was slightly but significantly greater than in fasted subjects, as indicated by comparative mean AUC values [201.4 ng.h/mL (fed) vs 172.5 ng.h/mL (fasted)]. Coadministration of a magnesium hydroxide/aluminum hydroxide antacid did not affect the bioavailability of the ondansetron tablet.