In order to reveal the vertical distribution of flame cells in a trematode cercaria, horizontal serial semi-thin sections were reconstructed by an image analyzer and a manual procedure. The ascending main excretory tubes extended forward, meandering up and down at the digestive system level from the excretory bladder. At the posterior end of the ventral sucker, they curved dorsally, passed through the dorsal side, returning to the mid level at the anterior end of the ventral sucker. They then ran forward to the posterior part of the oral sucker, and turned back. The flame cells were more abundant in the ventral region than in the dorsal region. The majority of pairs of right and left flame cells were present at the same distance from the digestive system or ventral (or dorsal) surface. This method, using conventional techniques, has some advantages for determining the horizontal and vertical distributions of flame cells in cercaria and may, therefore, promote research on cercaria.