The clinical trials of immunoscintigraphy with a cocktail of 131I anti CEA monoclonal antibody F(ab')2 and 131I anti CA 19-9 monoclonal antibody F(ab')2 (IMACIS-1) were performed to evaluate the safety and clinical usefulness. Thirty-five patients with proven cancer in six hospitals were examined in the phase two study. No significant changes of the heart rates, temperature, blood pressure, respiratory rates and clinical laboratory data were observed after i.v. IMACIS-1. Significant elevation of HAMA and IgE values in serum were not shown. Positive scintigrams which were interpreted by each hospital were obtained in 31/35 (89%) patients and in 39/53 (74%) lesions. The safety and clinical usefulness of immunoscintigraphy with IMACIS-1 were proven in the phase two study.