The California Air Resources Board (ARB) sponsored a 9-day field study for the intercomparison of methods for the measurement of carbonaceous aerosol species on the campus of Citrus College, Claremont, CA, in August 1986. As the quality assurance manager for the 1986 ARB-sponsored Carbonaceous Aerosol Methods Comparison Study, Environmental Monitoring and Services, Inc. distributed a set of “reference” aerosol samples to 13 laboratories for a comparison of different analytical methods for carbon. This paper describes the different reference samples used in the interlaboratory study and the analytical methods used by the different groups for their analysis. The analytical results from all participating laboratories are summarized in this paper. In general, the agreement between all laboratories for total carbon was within 20% for all samples. However, there were large interlaboratory differences in the organic carbon/ elemental carbon ratio for all samples, with the largest differences occurring of the automotive and woodsmoke dominated reference samples.