Glioblastoma (GB) represents the most aggressive brain tumor, which presumably develops from astrocytes. Ceonventional treatment such as surgery, radiation and chemotherapy, does not enhance poor prognosis and prevent the progression of the disease. Concomitant (adjuvant) therapy with natural substances is rather common way of treatment, where the signaling pathways is often unknown. In this thesis, we have investigated the influence of the natural cannabinoid cannabidiol (CBD) alone and in combination with chemotherapeutic temozolomide (TMZ) on signaling pathway that includes protein kinase ERK1/2, affecing proliferation, migration, invasion and apoptosis of glioblastoma cells. We found that the activated, phosphorilated ERK protein, in GB U87 cells, was reduced down to 43 % after treatment with CBD and to 20 % after treatment with CBD in combination with TMZ. CBD alone or in combination with TMZ did not have any impact on GB U373 cells.