The morphology of the convoluted testicular artery and the pampiniform plexus of the golden hamster was studied by light microscopy and corrosion cast techniques combined with scanning electron microscopy. The artery was found to be totally enclosed by the pampiniform plexus, except for minor superficial areas where the artery was exposed. Although no direct connection between the artery and the vein was found in the area of apposition, the arterial and venous walls reduced their thickness by sharing a single tunica adventitia, which seemed well suited to the transfer of substances by diffusion. Many band-like structures of the venous walls were found in the deep part of the spermatic cord, suggesting that these may act as barriers to slow down the venous blood velocity. The venous wall here and there showed a stick-like endothelial bridge, suggesting that it may prevent the veins from over distension. In addition to the close relation between the artery and the vein, lymphatic vessels and mast cells were distributed widely within the connective tissue of the arterio-venous walls and venous walls. Mast cells were situated mainly in the area of apposition, especially at the base of the protruding venous wall. These morphological findings suggest that mast cells may be involved in the counter-current transfer mechanism in the spermatic cord of the golden hamster.