Female C57/BL/6 x DBA/2 hybrid mice were exposed to two concentrations (270 and 135 ppm) of tetrachloroethylene (PER) in inhalation chambers for 6 h/day, 5 days per week, up to 11.5 weeks (270 ppm) and 7.5 weeks (135 ppm), respectively, followed by a 3-week exposure-free period. In the peripheral blood a reduction of lymphocytes/monocytes and of neutrophils was observed with an almost complete regeneration in the exposure-free period. A reticulocytosis during and also after the exposure indicated a compensatory reaction in the erythroid cell system. Bone marrow pluripotent stem cells (CFU-S) were not affected up to 7.5 weeks. Erythroid committed cells (BFU-E and CFU-E) did react, with a reduction of CFU-E numbers at 7.5 and 11.5 weeks. A slight reduction of CFU-C numbers at 7.5 weeks indicated, in accordance with the peripheral blood data, a disturbance of the granulocytic cell series as well.