The term phytoalexin proposed by Müller and Borger in 1940 was recently revised as follows ; “phytoalexins are low molecular weight, antimicrobial compounds that are both synthesized by and accumulated in plants after exposure to microorganisms”. This definition has often been used as synonym of “stress compounds”. The present review describes survey of historical ground of isolation, structure, biosynthesis, biological activity, and role in plant-disease resistance of representative compounds identified as or called “phytoalexins”. Structural characteristics of “phytoalexins” and varieties of stresses causing formation of “phytoalexins” indicate that one of the most important studies to be done on phytoalexins is isolation and characterization of key enzymes leading to initial formation of “phytoalexins” and, if possible, endogeneous elicitors rather than exogeneous ones.