We have used serial microangiography and radioactive 133Xe to study microvascular morphology and quantify blood flow in Walker 256 carcinomas implanted in rat tails during growth and immune rejection. No previous angiographic/quantitative studies during immune rejection are reported. Two tumor groups were identified. Group A grew rapidly, with a two‐ to six‐fold increase in blood flow, and caused death in 10 days. Group B grew more slowly, and increased blood flow two to four times. At 6 to 8 days postimplant the B tumors diminished in size; blood flow decreased and extensive lymphocytic infiltration developed. By 21 days all evidence of the tumor had disappeared. The rejection appears to be cell‐mediated, and the high incidence (65–70%) to be related to the number of tumor cells and/or presence of accumulated antigen in the innoculum. Microangiographic changes during immune rejection were specific, and included marked tortuosity of feeding vessels and a “ghostlike” fading out of tumor vessels, quite unlike the appearance of necrosis.

Summary Among the applications of diagnostic radiology in malignant lymphoma, G.I. examination and lymphography have been discussed. It is extremely important to accurately evaluate the extent of the lesion by use of radioisotopes as well as other X‐ray studies. Since the disease is characterised by a high radiosensitivity, adequate radiation therapy should result in some healing and a prolongation of life even in advanced cases. Diagnosis and treatment are quite intimately related in this disease.

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