Mycotoxins are secondary metabolites of moulds. They cause toxic effects in humans mainly by ingestion of contaminated food, and more rarely through inhalation or skin contact. Since mycotoxins are ubiquitous, they can do great damage to human health and that is the reason why the limits of mycotoxins' quantity in food should be set, so there could be no harm done to humans by ingestion of such food. Citrinin (CTN) is one of the first discovered mycotoxines, nevertheless it is still quite uninvestigated. Even though CTN was first recognised as a potential antibiotic, soon it was discovered to be nephrotoxic. Apart from nephrotoxicity, CTN is also suspected to cause immunotoxicity, genotoxicity and reproductive toxicity. In the absence of relevant data, it is impossible to determine total human exposure by food consumption, inhalation or through dermal exposure. The critical CTN concentration that would result in an exposure equal to the level of no concern for toxicity could not be determined either. The aim of this study was to determine cytotoxic concentrations of CTN in human adenocarcinoma cells A549 and hepatocellular carcinoma cells HepG2. Knowing the cytotoxic concentrations made it possible to calculate CTN concentration that is required to lower the cell viability of each cell line to 50% of maximum viability. The MTS assay was performed to measure the viability of cells after 24 h tretament with 10 different concentrations of CTN (0.1-200 µM). Concentrations of CTN that resulted in cytotoxic effect in A549 cells were 150 µM and 200 µM, and 100 µM, 150 µM and 200 µM in HepG2 cells respectively. Concentration of CTN that lowered the viability of treated A549 cells to 50% was IC50 = 228 ± 1.1 µM, and that concentration for HepG2 cells was IC50 = 139.2 ± 1.1 µM. In conclusion, CTN is twice as toxic to HepG2 cells comparing to A549 cells, suggesting that liver cells are more susceptible to toxicity of CTN than lung cells.