Objective In Hodgkin lymphoma (HL), tumor eosinophilia indicates poor prognosis, probably caused by eosinophil-induced stimulation of tumor cells. Our aim was to investigate the effects of eosinophil cationic protein (ECP) on HL tumor cells in vitro. Materials and Methods A fluorometric microculture cytotoxicity assay was used to measure the survival index of cells from the HL cell lines: HDLM-2 (T-cell origin, nodular sclerosis histology), KMH2 (B-cell origin, mixed cellularity), and L428 (B-cell origin, nodular sclerosis) after incubation with ECP97arg variants with different glycosylations and with ECP97thr. Flow cytometry monitored the effects of ECP on markers of cell death. Results For KMH2 and L428, ECP was cytotoxic with a dose−response relationship similar to a previously investigated small-cell lung cancer cell line. HDLM-2 was more sensitive to ECP at low concentrations, but reached a plateau (survival index of 70%) at 0.018 μM. The IC 50 for KMH2 and L428 were 0.2 and 0.15 μM, respectively. The IC 50 was never reached for HDLM-2. All tested ECP variants displayed similar activity in HDLM-2, in contrast to KMH2 and L428, which were more sensitive to less glycosylated ECP. Positive DNA staining (propidium iodide) of HDLM-2 cells treated with ECP indicated cell death by necrosis. Conclusions ECP is cytotoxic for HL tumor cells even at low concentrations, but heterogeneity between cell lines exists and not all tumor cells are eradicated. Two cell lines of B-cell origin, KMH2 and L428, were sensitive to ECP in a dose−response manner, but for HDLM-2, which is of T-cell origin, the cytotoxicity reached a plateau.