Summary:The detection and estimatinn of herbicidés uith ihe aid of Chtorelta: investigation of optimum conditions and iheir applicalion to the analysis of several herbicidesThe use of a uniform culture of Chlorella as yn inoculum at a given density under known conditions of temperature, light and nutrition in a gaseous mixture has allowed an improvement in the technique and given highly reproducible results. Tests with atrazine have shown that it can be detected at a dose or 0.012 ppm and estimated to an accuracy of 0.04 ppm. Other herbicides have been tested and their sensitivity was found to be in lhe following descending order: lerbutryne>lenacil = isoproturon>atrazine>chlortoluron>methabenzthiazuron = metoxuron