To the Editor.
—To estimate the human immunodeficiency virus (HIV) seroconversion rate among injection drug users (IDUs) entering a methadone treatment (maintenance or 21-day detoxification) program in Los Angeles, Calif, we retrospectively reviewed the records of all clients confidentially tested for HIV at one drug treatment center in Los Angeles between March 1989 and January 1994. All IDUs who had a negative HIV test when they first entered drug treatment, who had at least two HIV tests in the first or any subsequent treatment episode during the study period, and who had a history of injection drug use in the 12 months before they entered treatment were included in the analysis. The date of seroconversion was assigned as the midpoint between the last negative and first positive test. Seroconversion rate was calculated as the number of new HIV infections per 1000 person-years of observation.During the 56-month study period, 3931