Micronucleus (MN) formation in rat bone marrow and spleen erythrocytes was investigated following multiple intratracheal instillations of polycyclic aromatic hydrocarbons (PAHs). Male Sprague-Dawley-rats were dosed with up to 100mg/kg benzo(a)anthracene (56553) (BA), 34.1mg/kg dibenz(a,h)anthracene (53703) (DBA), or 10mg/kg dibenzo(a,i)pyrene (189559) (DBP) at 0, 8 and 16 hours. At 24 hours, bone marrow and spleen cells were collected. Erythrocytes were isolated from bone marrow and spleen samples. MN formation was assessed by the frequency of micronucleated polychromatic erythrocytes per 3,000 polychromatic erythrocytes (PCEs) scored. DBP was most toxic, followed by DBA and BA. A dose related induction of MN in bone marrow and spleen PCEs by BA was observed at doses over 25mg/kg. Significant increases in MN frequencies in both spleen and bone marrow PCEs were noted for DBA at or above 8.5mg/kg. MN frequency was significantly increased only in spleen PCEs by DBP at 10mg/kg. The authors conclude that all three PAHs are absorbed through the respiratory tract and their genotoxic metabolites are distributed in the bone marrow and spleen, that BA and DBA induced MN in both the bone marrow and spleen, and that the sensitivity of the spleen to the PAHs is similar or greater than that of bone marrow.