A method for determining chloroform, 1,1,1-trichloroethane, carbon tetrachloride, and trichloroethene in breath samples was developed. It consisted of collecting samples in 40-ml. glass-silanized tubes that were 16-in. long and had a 0.64-in. diameter. The ends tapered, resulting in a tube with a 1/4-in. diameter that was 1 3/4-in. long; each end had a shutoff valve attached. One end had a strip of rubber tube attached to the shutoff valve for collecting the breath sample, and the other end contained a 1/4-in. Swagelok nut with a rubber septum for withdrawing the sample. Samples were withdrawn using a pressure-lock, gastight syringe, and they were injected onto a gas chromatograph fitted with an electron-capture detector. The analytes were stable for at least 22 days in these tubes. The method detection limit was determined to be 0.03, 0.08, 0.04, and 0.04 pg/ml. for chloroform, 1,1,1-trichloroethane, carbon tetrachloride, and trichloroethene, respectively. Precision, based on 13 injections, was determined to be 13% for 0.09 pg chloroform, 13% for 0.21 pg 1,1,1-trichloroethane, 8% for 0.16 pg carbon tetrachloride, and 14% for 0.1 pg trichloroethene. In all, the proposed method is a sensitive and reliable one for determining volatile organic compounds in breath and a method that can also be applied to air sampling.