Up to now no standard cell culture model of the blood-brain barrier is available. However, several models based on primary cells or continuous cell lines have been characterized and described in respect of different applications. One of the most important characteristics of the blood-brain barrier is the restriction of paracellular transport, respectively its tightness. Human cell line ECV304 is one of the promising continuous cell lines for blood-brain barrier modelling due to two reasons: on the one hand the cells are able to form significant tighter layers than most of the other cell lines used and on the other hand several properties of the blood-brain barrier are inducible by using glioma-conditioned medium. Claudins are transmembranal proteins which form the backbone of the tight junctions at the blood-brain barrier. We have investigated the presence and inducibility of the expression of Claudin-1, Claudin-3 and Claudin-5 using immunofluorescence microscopy. For the first time this study proves the presence of Claudin-1, Claudin-3 and Claudin-5 in ECV304 (obtained from ECACC) cell layers and the inducibility of their expression by glioma-conditioned media.