Thirty-eight employees exposed to formaldehyde when working with acid-hardening lacquers and 18 nonexposed control persons employed at the same company were examined to determine lung function (spirometry and nitrogen washout), total immunoglobulin blood concentration, and work-related symptoms. The mean exposure to formaldehyde during an 8-hr workday was 0.40 mg/m3 air, and the mean exposure to peak values was 0.70 mg/m3. Mean exposure to solvents was low, i.e., approximately 1/10 of the hygienic effect. Eye, nose, and throat irritation was more common in exposed persons than in controls. Monday morning, after two exposure-free days, forced vital capacity (FVC) values were found to have declined by 0.24 L and forced expiratory volume in 1 sec (FEV1.0) by 0.21 L, compared with normal values. There was a weak correlation between the individual concentration of IgG and decrease in FVC and FEV1.0. No significant changes were noted in any other lung function variable before a workshift, and no lung function changes were noted over a full workshift. Deviations in FVC and FEV1.0 values did not correlate to peaks or mean exposures or employment time.