Extra-skeletal uptake of bone seeking radiopharmaceuticals has been documented by scintigraphy. We present a case of diffuse uptake of 99mTc-methylene diphosphonate (MDP) in the abdomen of a patient while undergoing continuous ambulatory peritoneal dialysis (CAPD) who had no symptoms or findings referable to the abdomen. We hypothesized that the 99mTc-MDP crossed the peritoneal membrane across a concentration gradient. An in-vitro simulation confirms that 99mTc-MDP will cross a semi-permeable membrane. Diffuse uptake of 99mTc-MDP may be a normal variant in patients on CAPD who have no signs or symptoms of peritonitis.