To clarify useful clinical parameters for determining the need for changes in antiretroviral regimens, 586 persons who were seropositive for the human immunodeficiency virus (HIV) and who had intermediate-stage HIV disease underwent follow-up semiannually for a median of 3.1 years after zidovudine monotherapy was instituted. The strongest predictors of time to the development of AIDS and of survival were an increased CD4 lymphocyte count (> 50/microL), a decreased neopterin level (> 2.4 nmol/L), and no increase in the number of symptoms after 7-12 months of zidovudine therapy. Men who had the best quartile CD4 lymphocyte and neopterin responses and who also had no increase in the number of symptoms were 23 times less likely to die (reflecting a 96% increase in survival) than were men who had the worst responses in these variable categories. After 7-12 months of zidovudine therapy, 5-year survival rates were 63% for men with good responses in all three variable categories, 47%-49% for those with good CD4 lymphocyte responses and good responses in one other variable category, 31% for those with only a good CD4 lymphocyte response, and 0 for those with poor responses in all three variable categories.