Formaldehyde is an ubiquitous industrial and indoor air pollutant to which millions are daily exposed. Because of the paucity of scientific data concerning the inhalation toxicity of this compound in humans, we determined the symptoms and alterations in pulmonary function resulting from inhalation for 1 h of 3 parts per million formaldehyde in a controlled environmental chamber. The protocol consisted of randomized exposure of each subject to clean air or 3.0 ppm HCHO on 2 separate days. Twenty-two healthy normal subjects engaged in intermittent heavy exercise (VE = 65 L/min) and 16 asthmatic subjects performed intermittent moderate exercise (VE = 37 L/min). Symptoms and pulmonary function were assessed during the time course of exposure; nonspecific airway reactivity was assessed after exposure. Both groups exhibited similar, significant (p less than 0.01) increases in perceived odor, nose/throat irritation, and eye irritation throughout the exposure. The normal group had the following statistically significant (p less than 0.02) lower pulmonary functions after 55 min of exposure to formaldehyde as compared to clean air: 3.8% in FEV1, 2.6% in FVC, and 2.8% in FEV3. The asthmatic group showed no statistically significant decrements in pulmonary function. Five of 38 subjects studied had decrements in FEV1 greater than 10%. In conclusion, acute exposure to 3 ppm HCHO produced: consistent irritant symptoms in both normal and asthmatic subjects, small decreases in pulmonary function in normal subjects engaging in heavy exercise, and clinically significant responses (defined here as decrements in FEU1 greater than 10) in 13% of the study population.(ABSTRACT TRUNCATED AT 250 WORDS)