Abstract: The biological screening for 24 herbicides in 15 different chemical classes with 9 different functions using Chlorella pyrenoidosa as a model biology, shows that this method for herbicide screening is very quick, simple,sensitive and more perfect than the Petri dishes method.Thus, the in vitro system can offer a second screening sieve to ensure that new potential lead structures will not be lost. Moreover, a set of biotests using Chlorella pyrenoidosa cell suspensions is suggested to form a herbicide prescreen in order to eliminate inactive compounds before the more expensive greenhouse screen on higher plants. The method has been shown to be suitable for the requirements for a microscreen and high throughput screening in vitro (HTS in vitro ).