The LeVeen peritoneovenous shunt (PVS) was investigated in 40 cirrhotic patients with refractory ascites. Five millicuries of Tc-99m-tagged human albumin microspheres (15-36 microns) were injected into the peritoneal cavity between the umbilicus and the left anterior superior iliac spine. The radiotracer was always detectable by scintigram in the lungs when the shunt was patent. In case of malfunction, by contrast, the radioactivity was either restricted to the venous tube or confined below the diaphragm for at least 4 hr. In the presence of complete obstruction, whereas the tube was not visualized after peritoneal injection, it was outlined by direct injection of 2 mCi of Tc-99m albumin microspheres into its subcutaneous tract, where it crossed the 12th rib, immediately above the valve. This technique sufficed to establish whether the site of obstruction was at the valve or in the tubing itself. In one patient, poor visualization of the tube and a delayed image of the lungs was caused by partial occlusion of the valve with fibrinoid debris. This radiotracer method proved simple, quick, and led to an immediate selective replacement when the shunt was not patent. Therefore, the use of this test is recommended for a definitive diagnosis, since there were neither false negatives nor false positives. No complications such as embolism or bacterial infection were encountered with Tc-99m human albumin microspheres, which are excellent tracers.