Colorectal cancer (CRC) represents a serious diagnostic and therapeutic problem at the global level due to its ever-increasing prevalence. It is a multifactorial disease, with a specific etiology for each patient, and a series of gene mutations over a longer period is required for the development of invasive cancer. Exosomes from colorectal cancer cells contain miRNA molecules that are associated with poor prognosis by promoting the proliferation, migration, and invasiveness of tumor cells. Furthermore, they represent a potential biomarker showing a significant correlation with the pathological state and progression of colorectal cancer. Liquid biopsy is a non-invasive method that can isolate circulating exosomes and miRNAs from a blood sample, which could lead to great progress in the early diagnosis of cancer as well as in its monitoring. The aim of this thesis is to compare the Qiagen and ThermoFisher methods for the isolation of RNA molecules from exosomes in patients with colorectal cancer. The initial sample is whole blood where exosomal RNA is isolated by precipitation and organic extraction from plasma exosomes. The concentration of the obtained RNA is determined spectrophotometrically, while the quality and integrity are determined by the capillary electrophoresis method. The expressions of reference genes B2M and PPIA were determined by the Taqman qPCR method, which determines the relative expression of the target genes. Additionally, the expression of the target miRNA (miR-19a-3p) is compared, as it is supposed to be elevated in patients with colorectal cancer and reference miRNA miR-103a-3p relative to “spike-in” miRNA UniSp6. In conclusion, there was no statistically significant difference between the Qiagen and ThermoFisher methods, therefore, the methods could be considered equivalent and either of the two can be used to determine miRNA expression without a significant difference in results. Despite the low concentration of isolated RNA, the samples are of sufficient quality to determine miRNA expression. Accordingly, the presence of reference (miR-103a-3p) and target (miR-19a-3p) miRNA is confirmed within all samples.