The regulation of inner-ear fluid homeostasis, with its parameters volume, concentration, osmolarity and pressure, is the basis for adequate response to stimulation. Many structures are involved in the complex process of inner-ear homeostasis. The stria vascularis and vestibular dark cells are the two main structures responsible for endolymph secretion, and possess many similarities. The characteristics of these structures are the basis for regulation of inner-ear homeostasis, while impaired function is related to various diseases. Their distinct morphology and function are described, and related to current knowledge of associated inner-ear diseases. Further research on the distinct function and regulation of these structures is necessary in order to develop future clinical interventions.