The cholinergic neurons in the laterodorsal tegmental nucleus (LDT) are involved REM sleep regulation. Since penile erection occurs during REM sleep, the role of the LDT in penile erection was examined in unanaesthetized head restrained rats. To detect penile erection, corpus spongiosum of the penis (CSP) pressure was measured through a telemetric device with simultaneous bulbospongiosum (BS) muscle EMG recording through stainless wires. Electrical stimulation in and around the LDT induced three CSP pressure patterns; 1) a full erection pattern indistinguishable from the spontaneous erection, characterized by a slow increase in CSP pressure with CSP pressure peaks associated with BS muscle bursts, 2) a muscular pattern characterized by CSP pressure peaks but in the absence of a vascular component, i.e., without an increase in baseline CSP pressure, 3) a mixed type response characterized by high frequency CSP pressure peaks followed by a full erection. Full erections were evoked in and around the LDT including more medially and ventrally. In the anterior half of the LDT, the sites for inducing mixed type events and full erections were intermingled, while they were separated in the posterior half. Muscular responses were evoked lateral to the sites for full erections. A CSP pressure response identical to micturition was evoked in and around Barrington’s nucleus and in the dorsal raphe nucleus. These results suggest that the LDT and surrounding region are involved in penile erection regulation. Moreover, different areas in the mesopontine tegmentum may have specific roles in the regulation of penile erection and micturition.