Three methods for quantifying test atmospheres of TDI, MDI, and their respective pre-polymers were compared in the laboratory: the modified OSHA 42 sampler, Tulane dichotomous sampler, and the ISO-CHEK™. Grouped samples (both 15-minute and 3-hour sampling periods) were collected from test atmospheres of the monomers ranging from approximately 2 to 20 ppb and of the pre-polymers ranging from 32.2 to 344.2 μg isocyanate/m3. In these tests, the Tulane sampler consistently yielded the highest results and accurately speciated the isocyanate into vapor and aerosol fractions. The OSHA sampler agreed with the Tulane sampler for MDI but reported lower concentrations of TDI. The ISO-CHEK™ consistently yielded the lowest results for isocyanate monomer and exhibited the highest variability, but it agreed with the Tulane sampler for short-term measurements of isocyanate pre-polymer. While not suitable for personal monitoring, overall the Tulane dichotomous sampler appears to be the most reliable of the devices for either short- or long-term sampling of reactive isocyanate vapors and aerosols.