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Perilymph is an extracellular fluid located within the cochlea (part of the inner ear) in two of its three compartments: the scala tympani and scala vestibuli. The ionic composition of perilymph is comparable to that of plasma and cerebrospinal fluid. The major cation in perilymph is sodium: The values of sodium and potassium concentration in the perilymph are 138 mM and 6.9 mM, respectively.
The inner ear has two parts: the bony labyrinth and the membranous labyrinth. The membranous labyrinth is contained within the bony labyrinth, and within the membranous labyrinth is a fluid called endolymph. Between the outer wall of the membranous labyrinth and the wall of the bony labyrinth is the location of perilymph.
Perilymph and endolymph have unique ionic compositions suited to their functions in regulating electrochemical impulses of hair cells. The electric potential of endolymph is ~80-90 mV more positive than perilymph due to a higher concentration of K compared to Na.
Perilymph is the fluid contained within the osseus labyrinth, surrounding and protecting the membranous labyrinth; perilymph resembles extracellular fluid in composition (sodium salts are the predominate positive electrolyte) and, via the perilymphatic duct, is in continuity with cerebrospinal fluid.
Syn: Perilympha [NA], Cotunnius' liquid, and liquor cotunnii.
Endolymph is the fluid contained within the membranous labyrinth of the inner ear; endolymph resembles intracellular fluid in composition (potassium is the main positively-charged ion).
Syn: Endolympha [NA], Scarpa's fluid, and Scarpa's liquor.
Clinical significance 
It has also been suggested that perilymph and endolymph participate in a unidirectional flow that is interrupted in Ménière's disease.
- Bosher SK, Warren RL (1968-11-05). "Observations on the electrochemistry of the cochlear endolymph of the rat: a quantitative study of its electrical potential and ionic composition as determined by means of flame spectrophotometry". Proceedings of the Royal Society of London Series B, Biological Sciences 171 (1023): 227–247. doi:10.1098/rspb.1968.0066. PMID 4386844.
- Konishi T, Hamrick PE, Walsh PJ (1978). "Ion transport in guinea pig cochlea. I. Potassium and sodium transport". Acta Otolaryngol 86 (1–2): 22–34. doi:10.3109/00016487809124717. PMID 696294.
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