The estrogen receptors alpha (ERα) and beta (ERβ) have been demonstrated in mouse models to be important for immune system regulation, and are differentially expressed in lymphoid organs. One ERβ splice variant, ERβ2, inhibits the ERα-mediated estrogen effect, and expression might predict response to selective estrogen receptor modulators. We studied the expression of ERα, ERβ1 and ERβ2 in peripheral blood mononuclear cells from 26 patients with chronic lymphocytic leukemia (CLL) and 30 normal controls using immunocytochemistry. ERα expression was generally low, while ERβ1 was expressed in 65% of patients with CLL and in 83% of controls (NS). In contrast, nuclear staining for ERβ2 was positive in 69% of patients with CLL, but in only 17% of controls (p < 0.001). In CLL, ERβ2 was found in B- but not in T-lymphocytes. Our data show the expression of ERβ1 and ERβ2 in the majority of patients with CLL, suggesting that the ERs are important in CLL and might be used as therapeutic targets.