Airborne measurements have been made in the emissions from several prescribed (deliberate) forest fires in Western Washington State. Particle measurements in the size range of 0.01 to 60 fim diameter show a multimodal character with the majority of the mass contained in particles between 0.1 to 1 pm in diameter. A particle emission factor (mass of particles produced per unit mass of forest fuel consumed) of about 4% was deduced for one of the fires. In addition to expected emissions of nitrogen dioxide, some of the fires appeared to be substantial sources of ozone. The fires were negligible sources of nitric oxide and sulfur dioxide.