In one human study, patients with AIDS or advanced ARC who received AZT had fewer life-threatening infections, improved in weight and performance, and lived longer than patients who received a placebo (inactive medication). Further studies are needed because toxic effects associated with the use of AZT were noted and the long-term effectiveness and toxicity of AZT are still unknown. It is also unknown if AZT will benefit patients with less severe HIV infections such as early ARC or PGL.