Summary The use of herbicides is claimed to negatively affect the environment and actually it does not represent an appropriate tool for the control of some weeds developing resistance. Allelopathic studies offer a challenge for discovering new lead compounds with new target sites. Then, they might be able to control the actual resistant weeds. A Standard Bioassay with selected Standard Target Species (belonging to both monocotyledonous and dicotyledonous species) is proposed to overcome the low reproducibility and the difficulties in comparing results from different research groups. This bioassay includes a commercial herbicide of known levels of activity. Herein, we illustrate this procedure with the results of studies performed with different plants belonging to wild and agricultural ecosystems that have rendered many allelochemicals belonging mainly to several terpene families.