From June 1988 to February 1989, we enrolled 36 patients with human immunodeficiency virus into a randomized double-blind placebo-controlled trial assessing the efficacy and toxicity of aerosolized pentamidine (AP) as secondary prophylaxis for Pneumocystis carinii pneumonia. Each patient underwent spirometric evaluations before and after aerosolized treatment. There was no significant difference in the results of baseline pulmonary function tests between the two groups. Eleven patients (65 percent) in the AP group developed cough but only four demonstrated significant reduction in the forced expiratory flow rates after AP; four patients (21 percent) in the placebo group developed cough, but no significant change in the expiratory flow rates was noted. All bronchospastic episodes were self-limited and symptomatically responded to remedial inhaled albuterol (salbutamol) treatment. We conclude that AP treatment is frequently associated with coughing attacks (65 percent), but the actual incidence of bronchospasm on spirometry is much lower (24 percent) and is generally quite mild.