Twelve male subjects were exposed to a toluene concentration of about 300 mg/m3 in the inspiratory air during rest and/or physical exercise on a bicycle ergometer. Each subject was exposed during four 30-min periods. Before exposure the subjects' body fat was calculated by means of underwater weighing and skeletal measurements. Needle biopsies of subcutaneous adipose tissue were taken up to 12 d after the exposure was concluded. The concentration of toluene in the adipose tissue was determined by gas chromatography after evaporation into nitrogen at a high temperature. After exposure at rest for 2 h, the mean concentration of toluene in adipose tissue was 0.7 mg (7.7 mumol)/kg. The corresponding value after 2 h of work at 50 W was 9.9 mg (109 mumol)/kg. There was a declining concentration of toluene in adipose tissue with an increasing degree of obesity. The half-time for toluene in adipose tissue ranged between 0.5 and 2.7 d. It increased with increasing amounts of body fat.