45CaCO3 was injected into guinea pigs, and the radioactivity in otolithic membranes of utriculi and sacculi, auditory ossicles and femora was determined by liquid scintillation spectrometry, to study the dynamic effect of streptomycin on calcium content of otolithic membranes, as a means to explore the mechanism of streptomycin ototoxicity. The results showed that otoconium was a dynamic structure which took up 45Ca in a time course generally comparable to that of bone. Saccular otolithic membranes showed greater intake than utricular membranes. The calcium ion concentration of saccular endolymph was greater than that of the utriculus and the two maculas were not identical. Streptomycin may influence 45Ca uptake in the two macular otolithic membranes, causes calcium metabolic disorder and a fall of otolithic calcium content. It is possible that the fluid environments of the endolymph have changed, therefore dysfunction of otolithic organ may occur. This hypothesis may be one of the explanation of the mechanism of streptomycin ototoxicity.