The effects of radioimmunotherapy were tested in xenografts of 2 different human pancreatic carcinomas comparing the intravenous and intratumoral application. On principle, intravenous injections of high doses of 131l-anti- Ca 19-9 or -BW 494/32 may inhibit tumor growth. In view of the low direct radiation dose (360-2100 rad), however, other factors than direct toxic effects have to be discussed, e. g. systemic effects due to the high whole-body irradiation. Intratumoral application, however, may induce tumor regression or growth inhibition due to the high local irradiation dose. Consequently, this treatment modality might be of clinical value at least in some patients.