Epidemiological studies suggest that consumption of diets containing fruits and vegetables, major sources of phytochemicals and micronutrients, may reduce the risk of developing cancer of the colon. Several phytochemicals and micronutrients present in fruits and vegetables are known to exert cancer-chemopreventive effects in several organs, including the colon. Monoterpenes such as d-limonene and perillyl alcohol derived from orange peels and lavender, respectively, have been shown to possess chemopreventive properties against mammary, liver, and/or lung carcinogenesis. The present study was designed to investigate the efficacy of dietary 40 and 80% maximum tolerated dose (MTD) levels of perillyl alcohol on azoxymethane (AOM)-induced colon carcinogenesis. The effect of this agent on the process of apoptosis in colon tumors was also investigated. Prior to the efficacy study, the MTD of perillyl alcohol was determined in male F344 rats in a 6-week subchronic toxicity study and found to be a 2.5-g/kg diet when added to the AIN-76A diet. At 5 weeks of age, groups of male F344 rats were fed control (AIN-76A) diet or diets containing 1 and 2 g perillyl alcohol/kg diet, representing 40 and 80% MTD levels, respectively. At 7 weeks of age, all animals except those in the vehicle-treated groups were given two weekly s.c. injections of AOM (15 mg/kg body weight/week). All animals were continued on their respective dietary regimen for 52 weeks after AOM treatment and then sacrificed. Colon tumors were evaluated histopathologically using routine procedures. Perillyl alcohol at the 1-g/kg level significantly inhibited the incidence (percentage of animals with tumors) and multiplicity (tumors/ animals) of invasive adenocarcinomas of the colon, whereas perillyl alcohol at 2 g/kg diet inhibited the incidence of total adenocarcinomas of the colon and small intestine as compared to the control diet. Our studies also indicate that the colon tumors of animals fed perillyl alcohol exhibited increased apoptosis as compared to those fed the control diet. These results demonstrate the potential chemopreventive activity of perillyl alcohol against colon carcinogenesis. The chemopreventive activity of perillyl alcohol is mediated through the tumor cell loss by apoptosis.