The characteristic operational features of different flowmeters and devices for measuring the coolant and feedwater flows in the loops of nuclear steam generating facilities (NSGF) currently operating in NPP are analyzed. A new design has been developed for labeled nuclear-magnetic flowmeter-relaxometers with a new flow measuring regime. This regime and other new structural solutions in the new devices have made it possible to perform measurements with accuracy to within <1%. The results of measurements of the flow and the longitudinal and transverse relaxation times for different fl owing media at different temperatures are presented. It is shown that the developed labeled nuclear-magnetic flowmeter-relaxometer is an expedient tool for monitoring the parameters of the coolant and feedwater in the NSGF loops.