The toxicokinetics of alpha-pinene were studied in human volunteers exposed by inhalation (2 h, 50 W) in an exposure chamber on four occasions. The exposures were about 10, 225, and 450 mg/m3 (+)-alpha-pinene and 450 mg/m3 (-)-alpha-pinene. The relative pulmonary uptake was about 60% for the higher exposures, and total uptake increased linearly with increasing exposure. The total blood clearance was high, about 1.11.h-1.kg-1. After the exposure was terminated, less than 0.001% of the total uptake was eliminated unchanged in the urine and about 8% in exhaled air. A long half-time in poorly perfused tissues indicates a high affinity to adipose tissues. There was a statistically significant exposure-response relationship among five subjects who experienced irritation. Short-time exposure to alpha-pinene did not give rise to acute changes in lung function 20 min after the exposure.