The interest in testing of water and wastewater for toxic compounds has increased in the last few years with rising pollutant levels from industry and with rising sensibility towards environmental problems. In order to get an early warning signal of environmental conditions the use of unicellular organism are recommended since they respond quickly and are easy to handle. An early warning system, called ECOTOX, for monitoring of water quality has been developed by a research group in Germany (Prof. D.-P. Häder). ECOTOX use movement parameters of the flagellate Euglena gracilis as orientation in the gravity field, the motility and the velocity of the cells. These parameters have been found to be sensitive to toxic compounds. In the present study it was shown that cadmium affect gravitaxis, motility, velocity and compactness of the cells negatively in the concentration interval of 10 to 15 mg l-1 after 24 and 48 h. After short time of incubation (minutes) with cadmium there is an inhibition of the different movements parameters starting at the concentration of 25 mg l-1. Like other biomonitoring systems ECOTOX can be used to detect changes in quality of aquatic systems.