The relationships between serum testosterone levels and somatosensory evoked potential (SEPs) latencies from the right and left posterior tibial nerves (PTNs) were studied in right-handed young men and women. The corrected P1 (P39) and N1 (N49) latencies from the right PTN (left hemisphere) were found to be significantly longer in females than males. The corrected P2 and N2 latencies from both PTNs were longer in females than males. Testosterone was not associated with N1 latencies. In females, there was a negative linear correlation between testosterone and latencies from the right and left PTNs. These relationships were complex in males depending upon foot and eye preferences. The following results were obtained from males: no correlation with P1, N1, and P2, but a direct relation with P2 from left PTN in total sample; in males with right eye and right foot preference, a direct correlation only with P1 from right and left PTNs; in mixed- and left-eyed males, inverse correlations with P1, N1, and P2 latencies especially from right PTN; in right-eyed males, direct correlation with P1, inverse correlation with P2 from left PTN; in right-footed males, direct correlation with P1 and N2 waves from right and left PTNs. The interpeak latencies also showed sex-related differences. The overall results suggested that the left brain would be the main target for testosterone effects in both sexes, which may be beneficial for females but mainly disadvantageous for males.