A number of single-domain antibodies (nanobodies) obtained previously to major marker blood proteins were tested as tools to preprocess urine samples from patients with bladder cancer. Nanobody-based tools demonstrated unique possibilities for noninvasive diagnostic studies along with other conventional methods, such as electrophoresis and, in prospect, mass spectrometric analysis. A testing of 22 samples from bladder cancer patients showed that the development of bladder cancer is accompanied by an increase in the urine contents of major blood proteins, including those known as potential bladder cancer biomarkers. New nanobody-based immunosorbents allow both specific enrichment and specific removal of particular antigenic proteins and subproteomes associated with them from a biological fluid. The isolation of immune complexes from the urine of a particular patient is of particular interest. An initial study of the complexes showed not only increased contents of IgA and IgG at advanced stages of the disease, but also many other components, which provide potential biomarkers of the pathological process in a particular patient. It is intended to use the approaches proposed in this work in a future larger-scale study of urine samples from patients with bladder cancer at different stages of the disease in order to identify new promising biomarkers of bladder cancer.