1. By treatment of the geometric isomers of 1,2-diphenylvinyllithium with mercuric chloride, the stereoisomeric bis(1,2-diphenylvinyl)mercurys have been prepared. 2. By the disymmetrization of the stereoisomeric bis(1,2-diphenylvinyl)mercurys, the stereoisomeric 1,2-diphenylvinyl mercury chlorides have been prepared. 3. An investigation has been made of the symmetrization of the stereoisomeric 1,2-diphenylvinylmercury chlorides with formation of the original bis(1,2-diphenylvinyl)mercurys. 4. A study has been made of the conditions required for the isomerization of cis-1,2-diphenylvinyllithium and of cis-bis(1,2-diphenylvinyl)mercury into the corresponding trans isomers. 5. It has been shown that the investigated exchange reactions occurring at the olefin carbon responsible for geometric isomerism are stereochemically pure and occur without change in the original configuration.