For the determination of the limits of the toxic concentrations MDCK, HEp-2, BGM and HeLa cells were cultivated in their growth period together with different dilutions (log 2-dilutions from 1240 g/ml to 0.1 g/ml) of the test substances at 37 ◦C and 5% CO2 for at least 5 days. Respective cell culture media without any test component were used as control (medium control).