Electrical activity of single neurons in the spiral ganglion of the guinea pig cochlea was correlated with receptor hair cell damage produced by local mechanical lesions of the organ of Corti. Damage to or loss of hair cells was assessed using scanning electronmicroscopy. Principal finds were (1) neurons emanating from damaged regions showed changes in their tuning curves such as loss of sensitivity, broadening of tuning curves; (2) in some cases, the loss of sharp tuning tip resulted in an apparent shift of the tuning curve to lower frequencies; and (3) apparently pure outer hair cell lesions, of limited spatial extent, could result in the same effects as mixed inner and outer hair cell lesions.