The purpose of this study was to investigate the differences in bio-potential in the stomach meridians of 20 normal healthy control subjects (NHC) and 20 patients with gastric disease (PGD). We measured changes in potential between ST-39 and ST-37 on the stomach meridian in response to invasive insertion of a needle at ST-36. The response patterns of NHC were regular in both the left and right meridians, whereas the response patterns of PGD were irregular. The potential of the NHC was significantly higher than that of the PGD group. The potential values in the left and right meridians of NHC were the same. However, the potential in the right meridian was significantly higher than that in the left meridian of PGD (p < 0.001). This study indicates that there may be changes in Qi or in the electrical properties of meridians according to health status, reflected in the regularity of the response to acupuncture or in the level of potential along meridians. Therefore, it may be possible to make a diagnosis from the state of a meridian by comparing levels of potential difference and its regularity.