Introduction: The cytotoxicity of anthelmintic agent, albendazole (ABZ) and its two major metabolites, sulfoxide (ABZSO) and sulfone (ABZ-SO₂), on non-hepatic Balb/c 3T3 line, two hepatoma cell lines (FaO, HepG2), and isolated rat hepatocytes was investigated. Material and Methods: Cell cultures were exposed for 24, 48, and 72 h to eight concentrations of the compounds ranging from 0.05 to 100 μg/mL (ABZ) and from 0.78 to 100 μg/mL (ABZ-SO and ABZ-SO₂). Three different assays were applied in which various biochemical endpoints were assessed: lysosomal activity - neutral red uptake (NRU) assay, proliferation - total protein contents (TPC) assay and lactate dehydrogenase (LDH) leakage assay. Results: The most toxic was albendazole whose EC₅₀ values calculated from the concentration effect curves ranged from 0.2 to 0.5 μg/mL (Balb/c 3T3) and from 0.4 to 73.3 μg/mL (HepG2). Rat hepatoma line and isolated rat hepatocytes were less sensitive to the impact of ABZ. Toxic action expressed as EC₅₀ was recorded after 72 h exposure only in LDH release assay at 0.8 μg/mL and 9.7 μg/mL respectively. The toxicity of metabolites was much lower. The most sensitive to ABZ-SO were fibroblasts and EC₅₀₋₇₂ₕ values were similar in all three assays used, i.e. NRU (14.1 μg/mL), TPC (15.8 μg/mL), and LDH (20.9 μg/mL). In the case of ABZ-SO₂ the mean effective concentrations were the highest, and could be reached only in one LDH assay. These values (μg/mL) were as follows: 65.3 (FaO), 65.4 (HepG2), 75.8 (hepatocytes), and 77.4 (Balb/c 3T3). Conclusion: The differences in in vitro toxicity of albendazole depend on metabolic ability of the cellular models. Primary cultured rat hepatocytes represent a valuable tool to study the impact of biotransformation on the cytotoxicity of drugs.