Direct contact method of autoradiography was applied in order to know in Eurytrema pancreaticum which was incubated at various intervals such as 60, 120, 240, and 360 minutes in the vitro media added with radioactive succinic acid, C(14)-succinate. The distribution of the radioactive succinate was clarified by this technique and possible explanation was presented. The autoradiographic procedures were essentially the same as those reported previously by Yoon et al. (1964). The most distinct autoradiograms were obtained after 240 minutes incubation. The radioactivity of this labelled succinic acid chiefly concentrated in reproductive organs, such as testes, ovary, egg containing uterine tubules and vitelline follicles.
