The performance and reliability of formaldehyde (50000) monitoring using the Model 3750/3751 3M Formaldehyde Monitor and the DuPont Pro- Tek Formaldehyde Badge were assessed in simulated sampling situations. Formaldehyde concentration was monitored in an exposure chamber by NIOSH method P-CAM-125, NIOSH method P-CAM-354, and a 2,4- dinitrophenylhydrazine assay. Experiments were conducted to determine the analytical recovery of the 3M monitor, to assess the sampling rate and capacity of both brands of monitors, to determine sample stability during the course of an exposure and to determine sample stability between exposure and analysis, and to determine the precision of the DuPont badges. The effects of formaldehyde concentration, exposure time, temperature, face velocity, relative humidity, chemical interference, and monitor orientation on badge performance were studied. Evaluation of the 3M Formaldehyde Monitor revealed a variable sampling rate and incomplete color development when using the manufacturer's recommended parameters. The quantitative reaction for analysis by the 3M monitor was significantly affected by absorbed water during storage and subsequent humidity in the exposure chamber. The DuPont Pro-Tek badge performed according to the manufacturer's instructions with limits set by interference, face velocity, and short sampling time. A blank correction was required. Industrial use of the DuPont badge required face velocities greater than 3 meters/minute, low phenol to formaldehyde ratios, and sampling times greater than 1 hour.