The rates of reaction of 2-chloro-and 2-bromo-1,l-diphenylpropene with ethoxide ions in ethanol have been measured titrimetrically in the temperature range 80-125".Both from the chloro-and the bromo-compound two reaction products have been isolated and identified : 2-ethoxy-1, l-diphenylpropene and l-diphenylmethylene-2-methylene -3,3diphenylcyclobutane. According to kinetic data and the ratio of products, the most probable mechanism is an elimination to the unstable 1, l-diphenylallene, followed by concurrent reactions of this molecule with itself or with ethoxide ion.