The oral bioavailability of high-dose metoclopramide was studied in 12 patients, who received oral or intravenous (i.v.) metoclopramide in random order with each of 2 consecutive courses of cytotoxic chemotherapy. The terminal half-life of metoclopramide was 7.1±0.4 h (mean±SEM) and was not affected by the route of drug administration. Mean bioavailability was 86.6±4.7% and the range (65–118%) was less than that reported for standard doses. Neither half-life nor bioavailability was significantly correlated with age. Adverse effects were mild and were similar for both oral and iv metoclopramide. Oral high-dose metoclopramide, given in the same doses as for i.v. administration, should therefore be as effective as the i.v. regimen and may be easier to administer.