The potential for use of compounds isolated from diverse sources, ranging from microbial to higher plants, has received increasing attention. These natural products represent a vast array of chemistries and mechanisms of action often having the requisite specificities to be ideal herbicides. Tentoxin, a cyclic tetrapeptide, has potent chlorosis activity on a variety of weeds of soybean and corn while not affecting these crops. Investigations into this toxin's mechanism suggest several enzyme target sites for the development of herbicidal analogues, each having the inherent specificity of the parent compound. Structure/activity relationships determined so far may permit a directed synthesis of efficacious analogues. New insights into biosynthesis of the toxin suggest possible means of increasing production to allow economical exploitation of the toxin itself as a herbicide.