Morpho logical, anatomical, and histochemical effects of S-ethyl dipropylthiocarbamate (EPTC) on Avena sativa var . overland were studied after treatment of seeds at various EPTC concentrations. The oat seed germination percentage was not affected by EPTC treatment. EPTC delayed initial root and coleoptile development at all concentrations used . Two or three days after treatment, however, the roots of seedlings treated with EPTC concentrations lower than 3 ppm grew at the same rate as the untreated seedlings and showed no abnormalities. Primary and adventitious root growth of seedlings treated with 3 ppm and higher was inhibited. Most of the adventitious roots remained in the radicle stage and failed to elongate. Bases of the roots became necrotic and were quite brittle . Formative effects were greater in the shoot than in the root. As result of treatment, coleoptiles became chlorotic, thickened, and were hard and brittle . The first true leaf of treated seedlings tended to adhere to the coleoptile and was broken as the coleoptile elongated . The complete shoot meristem of 12 ppm EPTC treated seedlings broke at the base . Young leaves formed within coleoptiles of treated seedlings oftain failed to emerge. His tochemica l studies s howed more carbohydrates in the coleoptiles of the EPTC treated oat seedlings than in those of the untreated seedlings . The lip1d-containing materials in the coleoptiles of the germinating oat seedlings disappeared from the coleoptiles of fully grm;n untreated oat seedlings , while they still persisted in the coleoptiles of 5-day-old EPTC treated oat seedlings. This suggests that EPTC might inhibit the breakdown and utili zation of stored foods .