Polychlorinated biphenyls (PCBs) are a group of compounds which have many industrial uses and have become an environmental pollutant. In the rhesus monkey, an unusual type of gastric hyperplasia has been produced by feeding the animals small amounts of these chemicals. By using a double contrast gastrogram with simultaneous pneumoperitoneum, we studied the development of the lesions radiographically. Over a period of several months the gastric abnormality progressed from minimal thickening of the gastric wall, with normal appearing mucosa, to extensive nodularity and irregularity in the area of involvement. This technique provides a method for studying the characteristics of the gastric hyperplasia over an extended time, and therefore has several advantages over autopsy studies or surgical biopsies. Although no similar lesions related to PCB exposure have been seen in humans, no survey of possible gastric changes has been done among persons exposed to these materials.