The maximum permissible concentration in air (MPCa) values for 239Pu02 are calculated on the basis of the generally accepted fatality rate during occupational hours. The risk of contracting cancer is taken instead of this fatality risk. The cancer induction risk to the bone, the lungs, the liver, and the tracheobronchial lymph nodes is examined. Two deposition and distribution models are used: the lung model presented in ICRP publication 19 and a modification of this model, which corrects for the influence of particle size on the rate of removal from the lungs. Our results indicate that reduction of the ICRP publication 2 MPCMa value by a factor of 7–70 is justifiable.