Amphiphysin (amph)Ⅰ, a protein concentrated in the nerve terminals, plays an essential role in clathrin-mediated endocytosis of synaptic vesicle membrane through an interaction with GTP ase dynamin. A speciffic antibody against amph Ⅰ revealed that the protein was also expressed in adrenal medullary cells. In the postnatal 11th day (P11) and adult rats, combined fluorescence histochemistry for catecholamine-containing cells with immunohistochemistry for amph Ⅰ disclosed strong and weak immunochemical signal of amph Ⅰ in noradrenalin (NA)- and adrenalin (A)-storing cells, respectively. Very strong immunoreactivity to amph Ⅰ was found in the intramedullary neurons but not in the adrenal cortex. In developmental stages, amph Ⅰ was discernible in the medullary chromaffin cells on 16th embryonic day (E16), E19, P0 and P2. Dopamin-β―hydroxylase (a catecholamine-synthesizing enzyme converting dopamin to noradrenalin) was immunohistochemically detected in the chromaffin cells during the parinatal periods. Colocalization of amph Ⅰ with dynamin was seen in NA-cells but not in A-cells. The present findings suggest that amph Ⅰ in the adrenal medullary NA-and A-storing cells is involved in membraine recycling mechanisms, which may be unique to each cell type, through endocytic activities.