The following species of the genus Fusarium have been cultivated on potatoes: F. avenaceum, F. coeruleum, F. sulphureum and F. solani. Only F. avenaceum grew well on the potatoes used by us. Cylindrical sticks were cut out from the potatoes at the locations with rot. These sticks were cut into discs of ca. 1 mm thickness which were extracted with ethyl acetate. The extract was purified by liquid-liquid-partition and used for the toxin-estimation by the chicken-embryo-assay. A significant mortality rate of 80--93% was found with the rotten potatoes. Similar mortality rates were observed with potato tissue adjacent to the rotten parts of the potatoes even though this tissue did not show any optical damage. Assuming that Fusarium-toxins caused the toxic effect the detection limit of the bio-assay-method lies at 0.5 ppm toxin (expressed as diacetoxyscirpenol-units).