We describe the results of treatment with zidovudine in 141 symptomatic HIV positive patients, 119 of whom had AIDS. Total mortality was 30% over a mean observation period of 45 weeks after the start of the treatment. This is much lower than the mortality among AIDS patients in the pre-zidovudine period. During the first 2 months the feeling of wellbeing and the body weight increased, but after 4 months these effects declined. Two months after start of therapy the number of new opportunistic infections declined, but it increased thereafter. Side effects were frequent: after 7 months zidovudine had to be reduced or even stopped in 43% of the patients mostly because of anaemia and/or leukopenia. After 6-7 months 45% of all patients had been given packed cells transfusions with a mean of 16 units. In general tolerability of zidovudine was better in patients with a higher number of circulating CD4-positive cells at the start. These results confirm that the effect of zidovudine in symptomatic HIV infected patients is favourable but only of limited duration.