The P2-purinergic receptor antagonists suramin, cibacron blue and basilen blue, the latter two being isomers of reactive blue 2, were studied for their effects on sound-evoked responses from the cochlea (cochlear microphonic, CM; summating potential, SP; distortion product otoacoustic emissions, DPOAE) and auditory nerve (compound action potential, CAP). Local application of these compounds (10-1000 microM) into the cochlear perilymph was associated with concentration-dependent response alterations. Effects of suramin on cochlear responses were minimal: High-intensity SP was reduced slightly at concentrations > or = 330 microM without significant alterations in CM or DPOAEs. The amplitude of the auditory nerve CAP was suppressed and its latency increased at drug concentrations > or = 100 microM. Cibacron blue and basilen blue were of greater potency in their effects on cochlear and auditory nerve responses. DPOAEs were generally reduced, low-intensity SP was reduced and high-intensity SP was increased and CM was little affected at drug concentrations 100-1000 microM. The CAP was suppressed and its latency increased at concentrations > or = 33 microM. Effects of suramin were largely reversible; those associated with cibacron blue and basilen blue generally were not. To the extent that these drugs acted selectively as antagonists of ATP receptor-mediated activity, results support the hypothesis that endogenous ATP exerts profound actions at the level of the cochlea and the auditory nerve.