Single potential analysis of cavernous electric activity (SPACE) is said to give information on the integrity of the central and peripheral parts of the autonomic nervous system insofar as it is involved in erectile function. A total of 30 patients who underwent radical prostatectomy with simultaneous severance of the cavernous nerves as treatment for locally advanced cancer were investigated by SPACE before and after the operation. The findings were compared to the those recorded on two different dates in 20 age-matched men who had not undergone surgery and in whom there was no evidence of any lesion of the autonomic nervous system. Even in this control group, few reproducible results were found. Nevertheless, with reference to the items "number of wedges" (i.e. monophasic elements with amplitudes of 25-100 microV) and "maximum amplitudes" of SPACE potentials there was a more than change correlation of the values on the two test dates, which was not found in the prostatectomy group. Although this difference between the two groups investigated was statistically significant, these findings cannot be interpreted as an effect of autonomic denervation of the cavernous bodies. This is attributed to the fact that the postoperative results in the prostatectomy group were more similar to the findings in the control group than to the preoperative measurements taken while the autonomic innervation was still intact. Therefore, our investigations lead us to conclude that routine application of SPACE as a direct check on the integrity of the autonomic nerve fibres involved in erectile dysfunction is not justified at present.