INTRODUCTION: The brain-derived neurotrophic factor (BDNF) is a protein belonging to neurotrophins that plays a key role in the proper development and functioning of the mammalian central nervous system. Previous studies have focused on assessment of the BDNF concentration in blood serum as a potential biomarker in neurological disorders. Recently, the BDNF signalling pathway has been recognised as a potential target for anticancer drugs, while its receptor (TrkB) as an oncogene in colorectal cancer cells. Despite the significant role in carcinogenesis, there are few studies on BDNF as a biomarker in colorectal cancer. MATERIAL AND METHODS: The study included 25 patients with clinically and histopathologically confirmed colorectal cancer, who were qualified for treatment. Prior to the first administration of chemotherapy, venous blood samples were collected from the patients and the biochemical parameters routinely determined prior to treatment were evaluated. Additionally, the serum BDNF concentration was determined by the immunoenzymatic method in all the patients. RESULTS: The serum BDNF concentration in patients was 50.24 ± 23.37 ng/ml. The BDNF concentration did not differ significantly between women and men. A negative correlation was found between the BDNF and CRP concentration and the BDNF and LDH concentration. The BDNF levels were significantly higher in patients who underwent primary tumour resection before chemotherapy. There was no correlation between the BDNF concentration and age, gender, BMI, CEA marker and liver enzymes in patients with colorectal cancer. There was no correlation between the BDNF concentration and clinical response to the treatment. CONCLUSIONS: BDNF cannot be considered as a prognostic factor in patients with colorectal cancer.