To the Editor: The Prospective Randomized Evaluation of DNA Screening in a Clinical Trial (PREDICT-1) by Mallal et al. (Feb. 7 issue) 1 showed that screening for HLA-B*5701 resulted in a significant reduction in the rate of hypersensitivity reactions (from 7.8% to 3.4%) among patients who were positive for the human immunodeficiency virus (HIV) and were receiving abacavir. However, because of methodologic limitations, this study will only modestly alter clinical practice. In the HLA-B*5701–negative group, all patients appeared to have a negative epicutaneous patch test (immunologic confirmation of a hypersensitivity reaction to abacavir). Notwithstanding the risks associated with rechallenge, 2 the investigators . . .