Separate sampling and analytical methods for the determination of diacetyl and acetoin have been developed to assess workplace exposures at a popcorn processing facility have been described. Diacetyl (NMAM 2557) is efficiently recovered from an Anasorb CMS sampler tube when the composition of methanol in the desorption solvent is 1%, and acetoin (NMAM 2558) is efficiently recovered when the concentration of methanol is increased to 5%. Desorption efficiencies for diacetyl and acetoin were acceptable, 89.9% (RSD = 0.018) and 94.9% (RSD = 0.019), respectively. Recoveries for nonanone, methyl ethyl ketone, and ethyl acetate were not optimized because they were present in very low concentrations in the popcorn processing facility and not considered to be major occupational health hazards. Samples were collected on Anasorb CMS solid sorbent tubes. All analytes were separated using a 30-m Stabilwax-DA fused silica capillary column, followed by analysis using gas chromatography with flame ionization detection. These methods were acceptable for monitoring and identifying exposures to diacetyl and acetoin present in the butter flavoring mixture used at popcorn processing facilities. For example, in the initial site visit the method was used to determine that maximum workers exposures to diacetyl (462.6 mg/m3), acetoin (59.1 mg/m3), and nonanone (0.45 mg/m3) occurred as the butter flavoring was added to the mixing kettle. When protective measures were recommended by NIOSH personnel and implemented bythe popcorn processing facility, the methods were then used to determine the effectiveness of these changes, which showed that diacetyl and acetoin concentrations had been reduced significantly to 0.97 and 2.3 mg/m3, respectively, while the concentration of nonanone fell to levels below the detection limit (LOD).