A review of 110 cases of colonic obstruction due to carcinoma demonstrated a variety of alterations in the distended colon on the plain roentgenograms. These findings were: predominantly fluid-filled distention; mottled fluid; accentuation of haustrations in localized areas; decreased haustrations; thickened septa; irregular septa; increased numbers of septa in localized areas; thickened colonic wall; and ragged inner colonic contour. Eighty-five per cent of the cases studied showed 2 or more of these findings. The only finding which correlated with the site of colonic obstruction was predominantly fluid-filled distention, which was seen in 76 per cent of the cases with lesions at or proximal to the splenic flexure and in only 13 per cent of those distal to the splenic flexure.Previous studies of experimental colonic obstruction in dogs and rabbits produced similar alterations in the experimental animal and allowed speculations as to the nature and significance of these alterations.Recognition of the alte...