Different hypotheses have been put forward trying to explain the mechanisms associated with the disruption of male sexual behavior after lesions of the medial preoptic area (MPOA). It has been suggested that sexual motivation, motor execution or both are affected by MPOA lesions. In the present experiment, the socio-sexual behavior of male rats bearing extensive MPOA lesions, that abolished sexual behavior, was compared with that of sham-lesioned animals and to prelesion levels. The socio-sexual interactions were recorded for 10 min in one prelesion and two postlesion tests. The frequency and duration of the following behaviors were recorded: rearing, sniffing, self-grooming, grooming partner, genital exploration, pursuit and resting. The analysis of the socio-sexual interactions showed that the frequency and duration of pursuit was reduced in the first and second tests after the lesion in comparison to both prelesion levels and to a sham-lesioned group. There is strong evidence that pursuit is the only precopulatory behavior that can consistently predict the appearance of sexual behavior. When pursuit is reduced the transition from the precopulatory to the copulatory phase is made more difficult. Therefore, it appears that the MPOA lesions reduce the subject's motivation to engage in sexual behavior.