A review with 40 refs. The aspartate metabolic pathway is responsible for the biosynthesis of lysine, threonine, isoleucine, and methionine in most plants and microorganisms. The absence of this pathway in humans and animals makes the central enzymes (aspartokinase, aspartate ß-semialdehyde dehydrogenase, homoserine dehydrogenase, and homoserine kinase) potential targets for inhibition, with the aim of developing new herbicides and biocides, and also for enhancement, to improve the nutritional value of crops. The current state of knowledge of these enzymes is reviewed, including recently detd. structural information and newly constructed bifunctional fusion enzymes.