Gene expression and content of the key enzymes involved in the synthesis of noradrenaline-tyrosine hydroxylase and dopamine beta-hydroxylase-was evaluated in the organ of Zuckerkandl of rats in the critical period of morphogenesis. High levels of mRNA and protein of both enzymes in the perinatal period of development and their sharp decline on day 30 of postnatal development were detected. These data indicate that the synthesis of noradrenaline in the organ of Zuckerkandl is maximum during the critical period of morphogenesis and decreases during the involution of this paraganglion.