A new analytical technique is described for measuring volatile sulphur compounds in human breath. The sulphur compounds were trapped and concentrated onto Tenax GC and then assayed by gas chromatography, using a specific sulphur detector. The detection limit amounts to about 0.2 ng/l (0.1 ppb). Among the sulphur volatiles, dimethylsulphide and methanethiol were quantitatively analysed in 100 ml of breath of 20 normal subjects and 35 cirrhotic patients. Dimethylsulphide in the breath of cirrhotics (113.4 +/- 31.9 ng/l, mean +/- SEM) was significantly elevated (p less than 0.05) compared with normals (21.1 +/- 1.7 ng/l). The concentration of methanethiol in the breath of normals and of most cirrhotics was less than 1 ng/l. In only five cirrhotics could methanethiol be detected in 100 ml of breath (3-23 ng/l). Dimethyldisulphide and hydrogen sulphide were not present in detectable amounts in the breath of normals. In cirrhotics, dimethyldisulphide was detected in a few cases. Ethanethiol was absent in the breath of both normals and cirrhotics.