Ultrasonic and radiological tests were compared in 267 patients suspected of having gall-stones. Radiological diagnosis was not possible in 20, because of lack of opacification, while in nine a gall-bladder was not demonstrable by ultrasound. In 226 the two tests coincided (positively or negatively), with 21 negative cholecystograms being interpreted as proof of stone. Seven of twelve discordant results were proven at operation: in three the ultrasonic, in four the radiological diagnosis was confirmed. Because of its accuracy, simplicity and absence of any risk ultrasonics is recommended as the first test to be performed if cholelithiasis is suspected.