Reports the findings of a study comparing the results of instruments measuring smoke particulate in real time to gravimetric samplers in Missoula and Hamilton, Montana, during the summer of 2000. Real-time, particulate monitoring instruments were evaluated to determine their accuracy when measuring smoke particulate concentrations from natural wildfires. Light-scattering instruments (Met One GT-640, MIE DataRAM, Optec NGN-3 nephelometer, and Radiance Research nephelometer) and light-absorbing instruments (Andersen RTAA 900 aethalometer) measured optical properties of the air to determine particulate concentrations. The Rupprecht & Patashnick Co., Inc. TEOM (tapered element oscillating microbalance) instrument was also included in the test. This ambient particulate monitor determines particulate mass concentrations by continuously collecting particulation on a filter and averaging the weight for 1-h increments. The real-time instruments were collocated with a U.S. Environmental Protection Agency federal reference method gravimetric sampler. Gravimetric instruments use filters to collect particulate. The filters are carefully weighted to determine the amount of particulate they have captured. This study indicates that results from real-time instruments can be corrected to estimate the particulate concentrations from burning biomass.