Human temporal bones obtained at autopsy from patients with various forms of sensorineural deafness are to be studied by microdissection and phase-contrast examination of surface preparations for correlation of audiological and pathological findings. Similar studies will be carried out in monkeys treated with ototoxic aminoglycosides and other drugs, for which complete behavioral audiograms have been obtained before, during, and after treatment. The patas monkey will be studied as a model for drug ototoxicity in man, because it alone among laboratory animals has been found to be susceptible to the ototoxic action of dihydrostreptomycin at dose-levels similar to those formerly used in treating human tuberculosis. Structure-activity relationships for various aminoglycosides, enzymatic modifications, and fragments, will be explored in guinea pigs, as will the possible relationship between salicylate ototoxicity and prostaglandin effects on the inner ear microvasculature. The question of potentiation of cochlear injury by combinations of aminoglycoside treatment and noise will be explored in monkeys. Temporary and permanent threshold shifts and accompanying cochlear changes will be examined in monkeys exposed to recorded industrial noise from automotive factories and to impulsive noise from power-actuated tools used in the construction industry.