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. The penetration of xylene was fairly rapid, peak concentrations appearing in the draining venous blood 4-6 min after exposure. 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.