In a greenhouse experiment a conventionally bred and a genetically modified (GMO) sugar beet variety were compared with regard to their tolerance to a selective (Betanal Progress EC; BP) and a non-selective (Liberty) herbicide, respectively. After the application of Liberty the Liberty-tolerant beets showed some chlorotic leaf spots, especially after higher dosages, but these spots became only partially necrotic. At all application rates tested, BP led to necrotic leaf spots which increased in number and intensity with increasing application rates, but no losses of plants were observed. The application of Liberty in highest amounts led to a 25 % reduction in calculated white sugar yield (WSY) when compared with an untreated control. After the application of BP at the same dosage, the WSY was only half for both varieties in comparison with the control. Different tissues contained the enzyme phosphinothricin-acetyl-transferase (PAT) in different amounts.