It was hypothesized that suppression of peripheral blood leukocyte subsets were markers of exposure to dietary deoxynivalenol (DON), a Fusarium graminearum mycotoxin in grain, at 1.0 mg kg(-1) but not at lesser doses in BALB/c mice. Groups of 10 female and 10 male BALB/c mice were fed 0, 0.25, 0.5, 1.0, and 2.0 mg kg(-1) DON for 14 and 28 days. Using flow cytometry with staining for leukocyte surface markers, the percentage of CD19(+) leukocytes (B cells) in peripheral blood was decreased in both sexes of BALB/c mice after 14 days of exposure to 1.0 or 2.0 mg kg(-1) DON, whereas exposure to DON over 28 days did not inhibit B cells compared to the control diet. The percentage of mononuclear cells in peripheral blood was decreased in female BALB/c mice fed 1 and 2 mg kg(-1) DON after 14 days compared with control diet. The percentage of CD11b(+) leukocytes (monocytes) in peripheral blood and total CD11b(+) splenic leukocytes were decreased only in female mice fed 1.0 and 2.0 mg kg(-1) DON after 28 days compared with control diet, which shows the greater sensitivity to DON in females compared to males. It was concluded that BALB/c mice adapted to DON exposure because peripheral blood cellular effects of DON at 14 days disappeared by 28 days with the exception of monocyte changes in females. This suggests that female sex hormones potentiate one potential marker of DON immunotoxicity in BALB/c mice.