Ten patients with CDC stage III of infection by HIV were treated with AZT at doses of 300 mg/day (100 mg tid). There were 5 males and 5 females, the median age being 40.5 yr' (range 26-46). Seventy percent of them had transfusion-associated HIV infection and the rest had been infected by the sexual route. A positive clinical response was observed in 100% of the group after 16-24 weeks of treatment: the Karnofsky performance status increased from 64% to 94% (p less than 0.01), the white blood cell count raised from 3.7 to 6.0 K/microL (p less than 0.01), the number of helper lymphocytes (CD4+) also raised significantly from 248.2 to 470.7/uL (p less than .01). Only two patients required red blood cells transfusions. The life expectancy at 82 weeks was 90%. Toxicity was both moderate and transitory. It is concluded that low doses of AZT (300 mg/day) produce similar clinical results as doses of 1200-1500 mg/day. A larger study is needed to support our preliminary findings.