AbstractWe conducted a prospective evaluation of pulmonary function and respiratory symptoms among 103 medical students exposed to formaldehyde over a 7‐month period to determine the incidence of bronchoconstriction and respiratory symptoms in response to exposure. Time‐weighted average formaldehyde exposures were generally less than 1 part per million (ppm) and peak exposures were less than 5 ppm. Acute symptoms of eye and upper respiratory irritation were significantly associated with exposure. There was no pattern of bronchoconstriction in response to exposure after either 2 weeks or 7 months. Twelve subjects had a history of asthma; they were no more likely to have symptoms of respiratory irritation or changes in pulmonary function than those without such a history. These findings are consistent with previous case reports that indicate exposure to formaldehyde vapor at levels that are commonly encountered in occupational and residential settings do not commonly cause significant bronchoconstriction, even among subjects with preexisting ast