Green algal cell suspensions are used in agrochemical research for screening herbicides. This paper reports on the inhibitory effects of 39 herbicides from 19 different chemical classes with nine different modes of action on green algae cultured in liquid media. The results show that herbicide screening using Chlorella as a model organism is simple, quick, and sensitive. In vitro systems can be a second screening net to ensure that potential new structures are not missed. A set of biotests using cell suspension cultures of Chlorella are suggested as a herbicide prescreen to eliminate inactive compounds before testing on higher plants in the greenhouse. The method has been shown to be suitable for the requirements of microscreen and high-throughput screening (HTS) in vitro. A large-scale microscreen has been devised, which cultures algal cells using self-made Erlenmeyer flasks containing 5 ml of liquid medium. They are particularly useful for HTS compounds with dissimilar modes of action.
