Seventeen kidneys removed from patients with renal carcinoma were submitted to ex vivo ultrasonography and then to serial pathological examination in an attempt to detect secondary tumours in apparently normal tissue. Ex vivo ultrasonography failed to reveal further tumours, but 2 lesions measuring 5 and 8 mm were found on pathological examination. These preliminary data suggest that intra-operative ultrasonography may be of little value in detecting secondary tumours in conservative surgery for renal carcinoma.