Sixteen patients with known neoplastic liver disease underwent 20 ultrasound examinations by two separate teams to determine the level of agreement in the measurement of lesion size and sonographic characteristics. The intraclass correlation coefficient for the observations on lesion size was r = 0.97 (95% lower confidence limit r = 0.96). We conclude that sonographic estimation of the size of neoplastic liver lesions in highly reproducible and that the measurements obtained may be safely incorporated into the criteria of response for cancer clinical trials.