in Tissues of Tumor-bearing Mice*

The amounts of arsonoazoalbumin-As74 containing varied amounts of label were fol lowed in tissues of tumor-bearing mice after intravenous injection. The uptake and clearance rates of this material were compared with those of uncoupled arsanilate-As74. In terms of arsanilate, the uptake of a label into tumor from azoprotein approached that of the uncoupled material only with the use of extensively labeled protein (30 moles arsanilate/mole protein) . Clearance of arsanilate-As74 was virtually complete in about 24 hours, whereas 2,5—50per cent of the initial concentrations remained in tumor 8 days following injection of arsonoazoalbumin-As74. Large, persistent accumulations of arsonoazoalbumin-As74 were found within liver and kidney even with as little as 1—2moles arsanilate/mole protein. These resemble the retention found after injeëtion of other dye proteins and curb possible clinical applications. The possibility ofovercomingthishandicapwithmore precise, minimal labeling exists. The uptake in kidney and the rate of disappearance of injected arsonoazoalbumin As74 from blood varied directly with the amount of arsanilate bound to protein (within the range 2—30moles of arsanilate/mole protein). The correlation between these factors was poor for liver and tumor and negative for muscle.