We treated 21 patients in a dose-finding and pharmacokinetic study of the monoterpene perillyl alcohol with the drug given orally in 3 divided doses on a chronic basis. The average number of days that patients remained on study was 48 (range 11-172). Fatigue and low-grade nausea were dose limiting. Using this schedule, a starting dose of 1.6 g/m2 with escalation to 2.1 g/m2 as tolerated is recommended. Two major metabolites were detectable and the mean peak plasma concentrations were 383 microM for perillic acid and 27 microM for dihydroperillic acid. The peak plasma concentration and the metabolite half-life were 2 h and 1 h post ingestion for perillic acid, and 4 h and 2.4 h for dihydroperillic acid, respectively. Stabilization of disease was observed in one of the 16 patients evaluable for response. Many of the gastrointestinal side effects that were poorly tolerated on a chronic basis may be partly related to the soybean oil base used in the current formulation. Further development of perillyl alcohol on this schedule would be facilitated by reformulation of the capsule.