Insular colonization is described in terms of simple Langmuirian equations for immigration and extinction. Possible techniques for the determination of the respective rate constants, k1 and k—1, of these processes, and of the transition times are discussed. The recolonization experiments of Wilson and Simberloff have been re—examined to illustrate some aspects of the model. The results show that k—1 is identical on five of the six islands throughout the period of regular monitoring. On the other island the same k—1 is observed initially, and later behavior may indicate the transition towards an assortive equilibrium. The effect of unobserved immigrations and extinctions on the experimental value of k—1 is of lower magnitude than previously suggested. The departure of the immigration process from "ideal" behavior is related to the defoliation damage produced by the defaunation. The species pool or source must be described by an activity" parameter, as well as by the number of species. In the experiments discussed, neither quantity is constant, and the effects of island area, and distance from source cannot be properly evaluated.