Free calcium concentration (CCa2+) profiles were evaluated in perilymph, endolymph, marginal cells, spiral ligament and blood serum of adrenalectomized (ADX) rats. Free CCa2+ was significantly greater in perilymph and significantly reduced in the serum of the ADX animals as compared to sham-operated animals. In addition, higher levels of free CCa2+ were found in the spiral ligament in ADX animals. Free CCa2+ did not appear to be affected by ADX in marginal cells and endolymph. These data suggest that marked reductions in endogenous levels of corticosteroids may have a systematic effect on free CCa2+ that is detectable in blood serum as well as cochlear fluids and tissues.