Five commercially available mass monitors were evaluated against aerosols of coal dust, silica, fiber glass, welding fume, oil shale, polystyrene latex, dioctyl phthalate, and fluorescein dye. The instruments were two identical TSI Corporation respirable aerosol mass monitors (RAMM), model 3500, and one each of GCA Corporation respirable dust monitors (RDM), models 101, 201, and 301. The RDM-201 was a long-term sampler (sampling up to 8 h), whereas the other monitors employed sampling periods generally 2 min or less. Each mass monitor sampled from uniform aerosol concentrations ranging from 10 mg/m/sup 3/. The aerosols were also sampled by three membrane filters collecting 2, 5, and 20 to 37 L/min. Mass monitor readings were compared to gravimetric concentrations of samples between 1- to 10-min duration. Statistical techniques were applied to determine significant differences between gravimetric and mass monitor results. The RDM-201 mass monitor displayed zero mass concentration of 27 of 73 measurements and an accuracy of +-74% for 27 other measurements, when gravimetric information indicated mass concentrations ranging from 0.3 to 5 mg/m/sup 3/. Accuracy of the other monitors was better than +-25% of gravimetric concentration when four or more instrument readings were averaged; however, individual readings differed from gravimetricmore » concentration as much as 300%. Particle size sensitivities of the monitors, indicated by the particle size of 50% measurement efficiencies, were 1.2- and 1.4-..mu..m aerodynamic diameter for the RDM-301 and -101, respectively, and 6-..mu..m aerodynamic diameter with poor efficiency. « less