Number of tumours (papillomas) produced by the application of 7,12-dimethyl benz (a) anthracene as initiator and croton oil promoter in mice were considerably inhibited (84%) by the prior application of eugenol. Moreover, there was considerable decrease in the number of tumour bearing animals and their onset. Eugenol inhibited superoxide formation and lipid peroxidation and the radical scavenging activity may be responsible for its chemopreventive action.