Despite of the fact that the impact of various stressful stimuli on catecholamine biosynthetic enzyme gene expression, activity and immunoreactive protein has been intensively studied, less is known about the aromatic L-amino acid decarboxylase (AADC), the enzyme, which catalyzes decarboxylation of L-dihydroxyphenylalanine to dopamine. We focused on the identification of AADC mRNA and immunoprotein in various mice tissues and detected both in selected mice neuronal tissues (adrenal medulla, sympathetic stellate and cervical ganglia) and also in non-neuronal tissues (liver, spleen, kidney and all four parts of the heart). Surprisingly, although we failed to detect AADC mRNA in mice thymus, lungs and abdominal fat, we found presence of the AADC immunoprotein in lungs as well as in the abdominal fat. We also tested the hypothesis, whether single or repeated immobilization stress can affect the AADC mRNA or immunoprotein levels in mice stellate ganglia. We revealed that single immobilization stress exposure did not affect the AADC mRNA or immunoprotein levels, while repeated immobilization stress produced significant elevation of both, AADC mRNA and immunoprotein levels in stellate ganglia. The aromatic L-amino acid decarboxylase is generally not considered to be limiting in regulation of the catecholamine biosynthesis. However, our data suggest a possible participation of this enzyme in the regulation of catecholamine biosynthesis in stellate ganglia of repeatedly stressed mice.