The use of direct reading aerosol instruments in industrial hygiene was considered. Commercially available portable instruments and aerosol research instruments were discussed. These included light scattering instruments, piezoelectric microbalance, condensation nucleus counters, oscillation microbalance, beta radiation attenuation monitors, aerodynamic particle sizers, and fibrous aerosol monitors. The recommendations arising from a recent workshop were discussed. The recommendations dealt with the development of a voluntary consensus standard on specifications, calibration and operation of direct reading aerosol instruments; the need for an accurate, portable, direct reading aerosol mass monitor; the providing of additional education and promotion in the industrial hygiene community to more fully use the capabilities of direct reading aerosol instrumentation; and the recommendation that manufacturers follow quality assurance guidelines in the manufacture of their instruments. Sampling efficiency and bias for direct reading instrumentation were discussed.