To the Editor: The review article by Hook and Marra (April 16 issue)1 on acquired syphilis in adults is informative and comprehensive. However, the recommendation to use a dose of 2.4 million units of penicillin G benzathine intramuscularly for primary, secondary, and early latent syphilis may not be the best advice. The authors cite Rein's review article,2 which reported that a dose of 2.4 million units of penicillin G benzathine results in treponemicidal levels of the drug in serum (>0.018 μg per milliliter) that last about three weeks. Original work by Collart and colleagues3 showed that in younger patients, treponemicidal… © 1992, Massachusetts Medical Society. All rights reserved.