The purpose of this study was to evaluate the ultrasonographic appearance and normal function of the ureter during gynecological surgery. The study group consisted of 14 gynecological patients scheduled for laparoscopy and 12 patients scheduled for laparotomy. Under standardized anesthesia conditions before pelvic surgery, the appearance, location, dimensions and peristaltic activity of the ureter were examined using a 7.5-MHz flexible laparoscopic linear transducer probe. Imaging of the ureter was possible in all cases. The ureteral lumen, mucosa, subepithelial connective tissue and muscular layer could be imaged as a tubular structure with low-level echoes. The separate layers, however, could not be differentiated by ultrasonography. The ureteral diameters at resting phase did not differ between the open surgery and laparoscopy groups. During peristaltic activity the maximal diameter was smaller in the laparoscopy group. The mean number of peristaltic waves was 23 +/- 7 waves per 5 min and this did not differ significantly between the open and laparoscopic surgery groups. Intermittent periods of retrograde flow were detected in 21 of the 26 patients. As seen in this study, ureteral location and function can be ultrasonographically evaluated during surgery and laparoscopic conditions do not have much influence on the ureter. The role of laparoscopic ultrasonography in lowering the incidence of ureteral complications in gynecological surgery needs further study.