The errors introduced by the instrumental noise in electrochemical noise measurements can be considerable and not easily detectable in certain conditions. Errors arising in the measurement of noise resistance in corrosion research are discussed, with special reference to the schemes analyzed and employed in two preceding papers.(1,2) Experimental examples are presented, showing how the impedance of the system under study, as well. as the frequency range of the measurements and the characteristics of the instrumentation used influence the magnitude of the errors.