Abstract
The growth of the EL^4^ lymphoma has been studied in thymusβdeprived, reconstituted and normal CBA/Lac mice. In normal mice the lymphoma grew slowly and progressively after intradermal injection, killing the host between 39 and 64 days later, depending upon the number of cells injected: no metastases were seen. In deprived mice the tumour grew more rapidly and killed all mice between 17 and 20 days: 50% had distant metastases. Reconstituted mice resembled normal mice. Intravenous injection of lymphoma cells was also followed by early death, within 16 days, of deprived mice: all had widespread tumour growth in the viscera. Normal and reconstituted mice survived considerably longer, some being free of tumour at over 200 days after injection; death was associated with localized tumour growth in soft tissues. Studies of the clearance of ~125~IUDRβlabelled tumour cells and an examination of early histological changes showed that this difference in the distribution of tumour growth was not due to differences in rate of clearance of cells from the blood or lungs. It appeared likely that the differences between thymusβdeprived and reconstituted mice were due to the survival of rather small numbers of tumour cells in a variety of tissues.