To the Editor: Whitley et al. (N Engl J Med 297:289–294, 1977) are to be congratulated on their careful clinical study. I strongly disagree, however, with their advice: “brain biopsy to establish diagnosis is necessary before initiation of therapy.” (The therapy advocated is adenine arabinoside [ara-A] to all patients for five days, with discontinuation of treatment in biopsy-negative cases after five days.) My reasons against biopsy include the fact that brain biopsy is not innocuous. It involves anesthesia in a very ill patient. Long-term effects, such as production of a seizure focus, cannot be ignored, especially in a young patient. © 1977, Massachusetts Medical Society. All rights reserved.