MATERIALS AND METHODS

In the present study, we have measured bone marrow radioactivity using direct counting of tissues from normal rats and from tumor-bearing nude rats after intravenous injection ofradiolabeled intact Mabs or F(ab')2 fragments directed against carcinoembryonic antigen (CEA). Radia tion doses to bone marrow and different organs were calculated from time course radioactivity distribution studies in normal rats. The results were also compared with dosimetric studies performed in tumor-bearing nude mice in the course of successful radioimmunotherapy (8, 9). A good correlation was found for all organsanalyzed in the two species. In mice, however, radiation doses to bone marrow could not be measured. A good correlation was also obtained with experiments performed on dogs, where bone marrow radioactivity was measured 24 hr after injection of ‘251-labeledirrelevant Mabs (6). These experiments should be helpful for clinical dosi metric calculations. Data obtained in one patient with colon carcinoma metastasis in the liver, who was injected with therapeutic doses o