The diagnosis of the diffuse intraperitoneal spread of ovarian or colorectal carcinoma (carcinomatosis) can be difficult when based on visual interpretation of immunoscintigraphic images alone. Twenty-nine patients with either colorectal or ovarian cancer were retrospectively evaluated by three technologists for carcinomatosis employing a quantitative analysis technique that compares uptake of In-111 satumomab pendetide (Oncoscint CR/OV, Cytogen Corp., Princeton, NJ) in a region of interest in the femoral vascular bundle to the uptake in two regions of interest in the lower abdomen, resulting in an uptake ratio (UR). All 29 patients underwent laparotomy after immunoscintigraphy. Of the 29 patients evaluated, 7 had histologically proven carcinomatosis obtained from the laparotomy. Using quantitative analysis, patients who did not have carcinomatosis had a mean uptake ratio of 1.12, and patients with carcinomatosis had a mean uptake ratio of 2.12. The differences between the means of these two groups of patients was statistically significant for all three technologists (P <.05). The results of this study indicate that there is a significant difference in uptake ratios between patients with carcinomatosis and those without it, and that quantitative analysis can be a useful adjunct to visual interpretation.