The Asian shore crab Hemigrapsus sanguineus is a recent invader of intertidal ecosystems along the western European coasts and the North Sea. In order to estimate whether this species is capable of colonizing the estuarine areas of the larger rivers, we studied the tolerance of the crabs towards extreme temperatures and salinities as they can appear in shallow tidal pools and during the outflow of riverine water, respectively. Individuals of H. sanguineus were incubated at salinities of 0, 10, 20, 30 and 40 and tem-peratures of 5, 10, 15 and 20°C. The animals were removed from the basins after 1, 5 and 10 days and tested for their ability to right into the normal position when turned on their backsides. Independent of the incubation time, all crabs showed average maximum righting times of up to 5 s at temperatures of 10, 15 and 20°C and salinities of 10 to 40. In freshwater, righting times were considerably extended at any temperature and mortality was high. Longer righting times were also observed at the lowest temperature of 5°C. Our preliminary results show that H. sanguineus is highly tolerant towards a wide range of temperatures and salinities which characterizes this species as highly adapted to changing environmental conditions. However, H. sanguineus cannot persist in fresh¬water conditions which prevents this species to colonize inner estuarine regions. Future studies on the osmoregula¬tion capacities and respiration rates will better define the thermal and osmotic limits of adult and juvenile Asian shore crabs.