We enrolled 1,353 subjects in a multicenter study to evaluate the spectrum of pulmonary complications associated with human immunodeficiency virus (HIV) infection and the feasibility of detecting pulmonary infections in asymptomatic members of this group. There were 1,171 who were HIV-seropositive; the remaining 182 were HIV-seronegative, but they belonged to high-risk transmission groups (homosexual/bisexual, or injection drug users). Single-breath carbon monoxide diffusing capacity (DLCO) was measured serially (at 3- to 12-month intervals) in a prospective fashion to determine whether a decline of > or = 20% predicted the presence of Pneumocystis carinii pneumonia or other pulmonary infections in the absence of new pulmonary symptoms and no new abnormalities on chest roentgenograms. In 64 subjects (6% of the group who had two or more measurements) DLCO declined > or = 20% from a prior value within 2 yr of entry, unassociated with fever, increased cough or dyspnea, or new chest roentgenogram abnormalities. Induced sputum was analyzed for the presence of P. carinii and mycobacteria in 44; fiberoptic bronchoscopy was performed with bronchoalveolar lavage in 14, six of whom also had transbronchial lung biopsy. All 64 subjects with the asymptomatic decline in DLCO were followed for an additional 3 to 12 months with additional clinical evaluations, chest roentgenograms, and DLCO determinations, or until death (one subject). In no case was the decline in DLCO due to P. carinii pneumonia or other pulmonary infection.(ABSTRACT TRUNCATED AT 250 WORDS)