:This paper discusses a non-intrusive acoustical diagnostic technique for assessing the wear and associated flow degradation of hydraulic pumps. The technique utilizes near-field airborne noise measurements to determine the acoustical energy emitted by the pump at various pumping harmonics. Ratios of the pumping harmonic noise levels are transformed into a Noise Wear Index. Data are presented which show the correlation between the Noise Wear Index and gear pump contaminant induced wear as indicated by a degradation of pump flow performance. The use of the Noise Wear Index for diagnosing system infirmities and improving system reliability is discussed.