Problems encountered using NIOSH Method 2520 for determining methyl- bromide (74839) in Florida in July were discussed. Method 2520 involved using two charcoal sorbent tubes containing 400 and 250 milligrams sorbent in series to sample methyl-bromide. After sampling, the tubes were desorbed with carbon-disulfide and the desorbate was analyzed for methyl-bromide by gas chromatography with flame ionization detection. Problems encountered included breakthrough, reduced adsorption capacity associated with high humidity, difficulty in preparing standard solutions, sample instability, changes in recovery with loading, and quantitation limit. Attempts to prepare reproducible standards for determining the capacity of the sorbent tube were unsuccessful. Using gas chromatography with atomic emission detection (GC/AEC) eliminated the need to prepare methyl-bromide standards, since other brominated compounds could be used as standards. Laboratory trials using a test atmosphere containing 27 parts per million methyl-bromide indicated that as the humidity was increased from 40 to 80 to 100%, the sample tubes capacity decreased from 122 to 23 to 1.6 liters. It was found that by placing a drying tube in front of the sorbent tube, the sampling volume could be increased without causing breakthrough. Storage stability tests indicated that storing sorbent tubes spiked with 5 to 233 micrograms (microg) methyl- bromide at -10 degrees-C for up to 1 week resulted in loss of analyte. The extent of methyl-bromide recovery decreased with decreasing loading. The author concludes that NIOSH Method 2520 has several problems significant enough to prevent its being included in the upcoming fourth edition of the NIOSH Manual of Analytical Methods. Modifications of the procedure recommended if it is necessary to sample for methyl-bromide include collecting a maximum sample volume of 1 liter unless a drying tube is used, storing samples at -10 degrees for no longer than 6 days, calibrating against brominated compounds other than methyl-bromide, and using GC/AEC for the analysis.