1. One thousand liver photoscans were analyzed, 410 called normal and 203 called positive but without positive proof of accuracy. The author believes that the accuracy of photoscanning in this group is fairly high. 2. A positive proof (biopsy, operation, or autopsy) of accuracy was obtained on 387 photoscans. Aspiration biopsy proved photoscanning accurate in 87 per cent, abdominal operation proved the accuracy in 71 per cent, and autopsy proved the accuracy in 72 per cent. The diagnosis was missed in 107 (27.6 per cent) of these 387 cases. 3. The most common causes for false positive diagnoses were: (1) the gallbladder fossa; (2) the thinned out or small left lobe of the liver; (3) extrinsic pressure defects of tumor; (4) porta hepatis: (5) pressure defect of vertebrae; and (6) peculiar shapes of the liver. 4. The most common cause for a false negative diagnosis was the inability to visualize the small (less than 3 cm.) metastasis on the photoscan. Several larger metastases of various sizes, including one 10 cm. lesion, were completely missed on the photoscan and noted later at operation or autopsy.