Terresterial plants produce a variety of secondary metabolites with different functions and biological activities under  normal  as well as stress conditions. The  metabolites produced under stress circumstances usually vary from those produced under normal conditions. The stress conditions could be either of the environmental changes, mechanical injury, nutrient  scarcity or surplus, and microbial invasion. Phytopathogenic fungi infect a healthy plant and produce  phytotoxins which cause disease in the host plant. Host plants after receiving chemical signals termed as elicitors from phytopathogenic fungi, produce chemicals called phytoalexins with fungitoxic  properties. Some plants however, contain ready made fungitoxic chemicals or closely related precursors easily changeable into fungitoxic principles which inhibit the growth of pythopathogens  and are called  phytoanticipins. The present review aims to describe the chemistry of phytotoxins, phytoalexins and pe-infectional antimicrobial substances taking into account the eco-chemical relations of phytopathogenic fungi with Leguminosae plants based on production of the secondary metabolites.