This study was designed to test the value of a multiparameter approach in evaluating perturbations in bone marrow and peripheral blood elements of mice exposed to ethylene oxide (EtO). Mice exposed to 255 ppm EtO for 6 hid were removed for analysis after 1, 2, 4, 8, and 14 d (sequential exposure) and 4, 6, 8, and 10 wk (5 d/wk). Prior to sacrifice, blood was removed from the orbital sinus for blood cell counts, hemoglobin determination, and hematocrit. A blood film was made for differential leukocyte counts. Bone marrow was flushed from femurs and tibias and counted, and aliquots were used for stem‐cell assay (CFU‐S) or flow cytometry (FCM) analysis. One aliquot of marrow was stained with propidium iodide for cell‐cycle analysis and another was reacted with fluorescein‐conjugated monoclonal antibody for B‐cell analysis. The preparations were analyzed for forward and 90° scatter and fluorescence on an Ortho 50H cytofluorograph. Perturbations of peripheral leukocytes occurred after one exposure. After multiple exposures, hematocrit, red‐cell number, and hemoglobin were generally depressed, with transient compensatory bursts, and bone marrow cellularity and CFU‐S were below normal. However, white‐cell numbers fluctuated dramatically during the exposure period. There was a shift in differential toward granulocytes, at times resulting in severely depressed numbers of lymphocytes in the peripheral blood. The FCM analysis showed an early depletion of granulocytes in the bone marrow followed by replacement and a relative lymphocyte deficit, especially pronounced at 10 wk. The B‐cell changes reflected general lymphocyte perturbations. Shifts in numbers of cells in S and CIM were observed, consistent with a moderate bone marrow response to cell loss.