Existing methods and instruments for online monitoring of the hemodialysis procedure, a method for determin ing the concentration of uric acid in dialysate by the level of spectral absorption at two wavelengths in the ultra violet region of the spectrum, the main characteristics and block diagram of an optoelectronic sensor based on a UVLED monitoring of the concentration of uric acid in the dialysis line of an “artificial kidney” apparatus, and analysis of results of clinical trials of the developed sensor are described.