The potential benefits of losartan (100mg daily) will be studied among HIV positive individuals over age 50 years whose CD4 counts remain ≤600 cells/mm3. Participants (n=110, 55 per group) will be randomized to receive losartan or matching placebo daily. After randomization, participants will start losartan (or placebo) at a dose of 50mg once daily, increasing to 100mg once daily at the 2-week study visit pending results of a week 2 toxicity lab evaluation (see 2.4 below for criteria). Following month 1, participants will return for follow-up study visit procedures at months 3, 6, 9, and 12.