Percutaneous absorption of m-xylene was studied in volunteer experiments by means of monitoring xylene concentrations in blood and in exhaled air, and urinary methylhippuric acid excretion Compared to normal working practices a rather extreme skin exposure, i e immersion of both hands in liquid xylene resulted in an estimated absorption of 35 mg xylene in 15 min which equals an estimated pulmonary retention within the same time period at TLV air level of 100 ppm The observed absorption rate for m-xylene was approximately 2 lg/cm 2 /min The penetration of xylene was fairly rapid, peak concentrations appearing in the draining venous blood 4-6 min after exposure. Further absorption took place for five hours, however, after the termination of exposure and the removal of the contaminant by alcohol and water rinsing. It was found, as expected, that venous blood from a contaminated area exhibits a much higher concentration of the contaminant than mixed venous blood To exclude this error in biological monitoring of xylene (and other skin penetrating solvents) exposure, exhaled air determinations are recommended As a sporadic finding in the investigation, a symptom-free subject with previous history of atopic dermatitis developed toxic eczema of the hands after xylene exposure and exhibited a three times greater absorption of the compound than the average for the rest of the group.