The relation between plasma concentrations and properties of lorazepam administered orally as premedication was studied in patients undergoing minor surgery. The drug was found to be reliably absorbed in most subjects producing plasma concentrations similar to those reported after injection. Effective concentrations were obtained within 30-60 min, maintained for 4-6 h and were closely related to the action of the drug on memory and its sedative and anxiolytic properties. Its kinetics were described in about half of the subjects by a one-compartment model, but in others two compartments were required. Variable half-lives were found (range 9.3-32.1 h, mean about 20 h). Sufficient drug remains after 24 h to suggest that residual c.n.s. effects may still be present.