Premature ejaculation (PE) has been thought to be psychological in the majority of patients. With few exceptions, organic conditions are rarely implicated. We investigated the possible role of sensory function in patients with primary PE to determine whether or not there is an etiologic basis for PE: We performed somatosensory evoked potentials (SEP) from the penis in 34 patients with primary PE and in 30 normally potent men. The latencies and amplitudes of the evoked potentials were measured by two different places in stimuli, with one at penile shaft (DNSEP) and the other at the glans penis (GPSEP). The mean latency of DNSEP was 1.51 msec. shorter in the patient group than the normal subjects, and the mean latency of GPSEP was significantly shorter (6.80 msec.) in the patient group than the normal subjects. The mean amplitude of GPSEP was lower than that of DNSEP in both groups. However, the mean amplitudes of DNSEP and GPSEP in patients with PE were significantly higher than that of normal subjects. With these results we conclude that patients with PE have a glans penile hyperexcitability. A glans penile hyperexcitability may give rise to an uncontrolled ejaculation, which is thought to be an organic implication for PE.