Fifty-eight AIDS patients who previously had Pneumocystis carinii pneumonia (PCP) were enrolled in an open trial of zidovudine therapy. We analyzed baseline clinical and laboratory parameters to identify predictors of outcome. Fifty-eight patients were followed for a mean of 26.5 weeks. There were 17 deaths; the probability of survival at 24 weeks was 0.81. Forty-one participants had unsuccessful outcomes, which included new opportunistic infections (24), progressive neurologic deterioration (2), and drug toxicity, excluding anemia, necessitating discontinuation of zidovudine (15). Only 24 subjects (41%) were receiving zidovudine at the end of the study period including 17 who had neither opportunistic infection nor toxicity. Low baseline hemoglobin level (p less than 0.001) and poor performance status as measured by the Karnofsky scale (p less than 0.01) independently predicted unsuccessful outcome and early death. Low hemoglobin (p = 0.001), low platelet count (p = 0.016), and increased time since PCP (p = 0.008) predicted development of drug toxicity. Neither CD4 lymphocyte count nor p24 antigenemia correlated with outcome.