1. Applied potential tomography is a new, non-invasive technology for observing changes in blood volume. We have used it to study 12 women with lower abdominal pain caused by pelvic congestion, and 15 control subjects. 2. A significant increase in blood volume of 1.8% was observed in the pelvis of women with congestion when changing from the supine to the erect position, and of 2.7% in the control subjects (P less than 0.0002). The difference between the groups was not significant. 3. The distribution of the area over which blood volume changes took place was significantly different between the two groups (P less than 0.002). More of the posterolateral part of the pelvis was involved in women with pelvic congestion than in the control subjects. 4. Applied potential tomography distinguishes between normal women and those having pelvic congestion with a specificity of 87% and a sensitivity of 75%.