The purpose of this study was to compare the results of airborne organic fiber measurements using different collection modes and counting techniques. Atmospheres of p-aramid or cellulose respirable fiber-shaped particulates (RFP) were generated in an inhalation chamber. For each experiment, 30 filters (10 gold-coated polycarbonate filters, 10 methyl cellulose filters, and 10 methyl cellulose filters and corresponding cowls) were exposed to fibrous aerosols at concentrations ranging from 25 - 50 f/cc. Subsequently, attempts were made to count and compare each of the filters by three optical techniques, namely light microscopy (LM) (PCOM- NIOSH 7400) scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Preliminary results demonstrated that the gold-coated polycarbonate filters were not appropriate for counting by LM and TEM. In addition, washing the cowl onto the same filter did not contribute greater numbers of fiber counts and seemed to facilitate clumping. When comparisons were made between LM, SEM, and TEM counts on the same filters, the fiber numbers were not significantly different when evaluated via the different analytical techniques. These findings are in contrast with the preliminary data of other investigators who have reported a 2-5 x increase in the numbers of organic fibers when counted by SEM vs. PCOM. Studies are ongoing to resolve the differences between analytical methods for counting organic fibers.