Most of the measurements concerned formaldehyde and wood dust. The other substances measured included terpenes, solvents, and heptachlor. Before 1975 the formaldehyde concentration regularly exceeded 2 ppm during many workphases. Considerable improvements in ventilation and the composition of glues have occurred since then, and today the exposure level is below 2 ppm during most workphases. High peak concentrations, 20-30 ppm at the highest, were characteristic of exposure in earlier years. The concentrations of wood dust have also decreased, eg, from over 5 mg/m3 to 1 mg/m3 or below during forming. These data have been used to evaluate past exposures in an epidemiologic study on cancer risks in the particleboard, plywood, and sawmill industries.