Seventeen single-photon emission CT (SPECT) studies were performed after intraperitoneal administration of 99mTc-sulfur colloid in patients with a history of colon cancer to assess the extent of intraperitoneal fluid distribution prior to intraperitoneal chemotherapy. Planar gamma images were also obtained in all patients for correlation with the SPECT findings. Four patients had transmission CT scans of the abdomen after intraperitoneal administration of iodinated contrast material. In seven patients, repear planar and SPECT studies were performed with the original or a different infusion volume to determine if different volumes altered the fluid distribution qualitatively or quantitatively (using a linear profile method). We found that 360° peritoneal SPECT is easily performed after intraperitoneal administration of 99mTc-sulfur colloid. SPECT provides more detailed anatomic information than planar scans do. Spaces of the upper abdomen, such as the lesser sac, were resolved better with SPECT than with planar imaging. SPECT assessment of intraperitoneal fluid distribution also correlated well with transmission CT scans. Quantitative linear-profile radionuclide plots were reproducible at the same volume and showed no major differences in relative intraperitoneal fluid distribution between the 1.5- and 3.0-l infusion volumes, suggesting that the two delivery volumes were equivalent in relative distribution. SPECT appears to be a useful procedure to define the extent and location of intraperitoneally administered fluids. Thus, it may be of value in determining the intraperitoneal distribution of drugs and radiopharmaceuticals used in the treatment of intraabdominal tumors.