Due to the worldwide epidemic of acquired immunodeficiency syndrome (AIDS), the past ten years have witnessed a flurry of activity in the chemotherapy of viral diseases. Unprecedented scientific efforts have been made by scientists and clinicians to combat infections of human immunodeficiency virus (HIY), the causative agent. Looking back over the past ten years, we have made remarkable progress toward the treatment of the viral disease: isolation of HIV only two years after the identification of the disease, plus major strides in the areas of the molecular biology and virology of the retrovirus, etc. More remarkably, the discovery of the chemotherapeutic agent AZT (Retrovir) was made within two years after the isolation and identification of the virus, followed by unprecedented drug development efforts to culminate in the FDA approval of AZT in twenty-three months, which was a record-breaking time for approval of any drug for a major disease. The last six to seven years have particularly been an exciting and productive period for nucleoside chemists. Since the activity of AZI' was established in 1985, nucleoside chemists have had golden opportunities to discover additional anti-HIV nucleosipes, which are hoped to be less toxic and more effective than AZT, and the opportunity continues. As we all are aware, AZT possesses extremely potent anti-HIY activity, and no other nucleoside or non nucleoside has surpassed the potency of AZT in vitro.