Consumption of lycopene has been associated with reduced risk of prostate cancer. We have investigated the effects of lycopene, fed as a lycopene-rich tomato oleoresin (LTO) at two doses, on in vivo mutagenesis in prostate, colon, and lungs of lacZ mice. Both short-term benzo[a]pyrene (BaP)- induced and long-term spontaneous mutagenesis were monitored. Non-significant inhibition of spontaneous mutagenesis in prostate and colon was observed at the higher dose of LTO, and the observation of inhibition in colon was facilitated by an unusually high spontaneous mutagenesis rate. BaP-induced mutagenesis was slightly inhibited by LTO in prostate. However, enhancement of BaP-induced-mutagenesis was observed in colon and lung. These results indicate that any antimutagenic effects of LTO may be organospecific.