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HAMBERGER, BERTIL, MARTIN RITZN AND JAN WERSALL: Demonstration of catecholamines and 5-hydroxvtrvptamine in the human carotid body. J. Pharnuuol. 152: 197-201, 1966. Human carotid bodies were examined with a fluorescence method for histochemical visualiza-tion of certain monoamines. Cells with a green to yellow-green fluorescence containing catecholamines, presumably norepinephrine, and yellow fluorescent cells containing 5-hydroxytryptamine were found. The presence of the two monoamines was established by fluorescence microspectrophotometrv. Though the chemosensorv function of the carotid body is now generally recognized, the cvtochemical basis of this function is still the sub.ie(t of much discussion. The varying chromaffinitv in certain species suggested that the glomus cells contained a phenolic amine, presuniably epinephrine (see Watzka, 1943; Adams, 195S: Pryse-Davies et al., 1964). How-ever, the chromaffin reaction has an extremely low sensitivity and specificity, and it has not l)een possible to locate and establish the nature of any presumptive phenolic amine. The l)eS-ence of norepinephrine (NE) has been detected biochemically in the carotid body of the calf (Muscholl et al, 1960), and Prvse-Davies et al. (1964) have found catecholamines in a single human carotid body. In the present study, human carotid bodies were examined by the fluorescence method of Falck and Hillarp (Falck et al, 1962; Falck, 1962: Corrodi and Hillarp, 1963, 1964), which demonstrates the cellular (list ribut ion of certain monoamines, including epinephirine, XE an