Following the occurrence of metal fume fever in some subjects after the installation of an electric furnace in a steel plant, a survey was undertaken to examine whether subjects exposed to fumes containing zinc oxide would exhibit a detectable impairment in ventilatory function, and whether a forced oscillation technique (FOT) was more suited for this detection than conventional spirometry. Pulmonary function measurements were made in 57 exposed workers (production or maintenance) and 55 nonexposed workers (maintenance or strandcasting department) at the beginning and near the end of a work shift (day or night). Maximal expiratory volumes and flows were measured by means of a pneumotachograph, and respiratory resistance (Rrs) and reactance at various frequencies by means of a FOT. These measurements were repeated 1 day later. During the day shift, there were no significant differences in pulmonary function between exposed and control workers. However, during the night shift, an influence of exposure on pulmonary function was revealed both by spirometry and by FOT: workers exposed at night showed a slight decrease in vital capacity (VC) and in forced expiratory volume in one second (FEV1), and a decline in respiratory resistance (Rrs) with oscillation frequency, that were more marked than in unexposed subjects. In contrast to the frequency dependence of Rrs, the changes of lung volumes and expiratory flows were related to differences in initial values between exposed and nonexposed workers. The decrease in FEV1 was maintained the day after exposure. The forced oscillation technique proved at least as sensitive as spirometry to detect small across-shift changes in ventilatory function. Although the effects on pulmonary function were small, it is likely that they represent a subclinical response to the inhalation of small quantities of zinc oxide.