The distribution of adrenal chromaffin cells in the control beagle dog was investigated. The presence of chromaffin cells in the adrenal medulla, three zones of the adrenal cortex and capsule was identified by staining with H&E, chromium salts and TH (tyrosine hydroxylase) antibody. With H&E stain, there are morphological differences among the chromaffin cells in the medulla, cortex and capsule. In addition, the number of the capsular chromaffin cells was statistically significantly decreased in the 8–9, 11–12 and 15–16 month age groups compared with the 5–6 month age group. Both medullary and extra-medullary chromaffin cells contained catecholamines, demonstrated via special staining for chromium salts. TH is the first enzyme in catecholamine biosynthesis; it is a useful maker for all cells involved with catecholamine biosynthesis including chromaffin cells. TH antibody confirmed that the extra-medullary cells were chromaffin cells. Terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay for detecting the apoptotic signalling identified the apoptosis of the chromaffin cells in the capsule.