The influence of selective REM sleep deprivation on masculine sexual behavior has been a matter of controversy. In the present study, the sexual behavior of male rats was analyzed in subjects deprived on REM sleep by the island technique for 24 or 16 h daily during 20 days. When compared to control rats, both groups displayed changes in sexual performance since the first day. The effects were: an increase in mount, intromission and ejaculation latencies and in mount frequency as well; a decrease of ejaculation frequency and of the Hit rate. The effects became stronger as REM sleep deprivation progressed. Rats deprived of REM sleep for 24 h were extremely debilitated after 12 days and some of them died, whereas the rats REM deprived for 16 h remained healthy during the 20 days. These data indicate that REM sleep deprivation interferes with the mechanisms that regulate male sexual behavior.