Scanning microscopy was used to examine guinea pig cochleas for structural damage immediately after exposure to a pure tone ranging from 96 to 129 dB SPL. Functional changes to the cochlear neural sensitivity were assessed using the N1 audiogram. Principal findings were: (1) The order of damge to receptor cells with increasing sound intensity was OHC1, then IHC, then OHC2 and OHC3. (2) The spatial distribution of damage to OHC1 and IHC differed with IHC tending to show damage mainly in the vicinity of the exposure frequency location and OHC1 damage spreading basalward of this point. (3) N1 threshold losses spread progressively to lower frequencies as exposure intensity increased. This was accompanied by an apical spread of damage to the receptor cells.