Sandalwood oil (SW oil) has been used for the treatment of inflammatory and eruptive skin diseases. In the present study, the chemopreventive effects of SW oil on 7,12-dimethylbenz(a)-anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate(TPA)-promoted skin tumour development and TPA-induced ornithine decarboxylase (ODC) activity in CD1 mice were investigated. Female CD1 mice (5–6 weeks old) were divided in different groups, having 30 mice in each group. One week after topical application of DMBA (200 nmole in 100 μ l acetone) alone or with SW oil at different concentrations (100 μl, 1.25, 2.5, 3.75, 5% in acetone), at different times (0.5, 1, 2 h) before DMBA, the mice were treated topically with TPA (5 nmole in 100 μl acetone) alone or with SW oil at different concentrations (100 μl, 1.25, 2.5, 3.75, 5% in acetone) at different times (0.5, 1, 2 h) before TPA applications twice a week for 20 weeks. The mice were weighed and papillomas counted weekly. The results indicate that SW oil pre-treatment decreased the papilloma incidence and multiplicity in a concentration and time-dependent manner. The pre-treatment with 5% SW oil (100 μl) 1 h before DMBA and TPA treatments provided a maximum of 67% and 96% decrease in papilloma incidence and multiplicity, respectively, after 20 weeks of promotion. The mice pre-treated with SW oil at all concentrations and time period before TPA had significantly lower ODC activity than the group treated with TPA alone. The data suggest that SW oil could be an effective chemopreventive agent against chemically-induced skin cancer.