In order to assess the efficacy and the toxicity of zidovudine in AIDS patients, we have studied, prospectively, 117 patients that were treated with this drug, in several andalusian hospitals between January 1988 and June 1990. Initial dose of the drug was 200 mg every 4 hours. Mean survival was 100% at 6 months and 66.5% at 23 months. Survival at 19 months was higher in ADVP (77%) than in non-ADVP (48%). A positive influence on weight. Karnofsky index and number of opportunistic infections during the six first months of treatment was recorded, benefit that was lost progressively from that moment onwards. Main adverse effects were hematological, 10.1% of the patients requiring transfusions due to hemoglobin lower than 6.5 gr%. The more frequent cause to stop therapy was severe neutropenia (less than 500 neutrophils per mm). We consider that the beneficial effect of zidovudine is only transient, diminishing gradually when the treatment is prolonged. At present doses adverse effects are moderate not being present in most of the patients.