The reasons for failure of the interspecific cross involving Vigna mungo as ovule parent and Vigna radiata as pollen parent was studied by in vitro, in vivo and bio-chemical methods. In vitro germination of pollen in media supplemented with stigma extract indicated that some chemical principles in V. mungo stigma reduced germination of V. radiata pollen. In vivo germination studies showed that there was disintegration of pollen tubes throughout the stylar region. The disintergrated tubes ended in callose plugs. Some of the pollen tubes gained entry into the micropylar end, but were subsequently obstructed at the point of their entry and hence fertilization was not successful. Biochemical studied confirmed the existence of pre-fertilization barriers.