THE FREQUENCY with which carcinoma of the lung metastasizes to the brain has been a matter of interest during the past twentyfive years. Dosquet,1in 1921, published one of the earliest reports on this subject, and Tinney and Moersch,2in 1944, presented one of the latest. The latter authors have summarized various opinions on the subject. The incidence of intracranial metastasis from carcinoma of the lung is variously given as from 16.5 per cent (Ochsner and DeBakey, 19423) to 36.3 per cent (Olson, 19354). The average figure compiled from several sources is 23 per cent. The accepted theory for the frequency with which the brain is the site of metastasis is based on the fact that carcinoma cells can enter the blood stream without passing through the capillary filter of the lung and are thus more likely to reach the brain. That the usual prognosis for