In this paper we investigate the degree to which the internal migration flows in Western Germany can be related to employment changes. The data consist of in- and out-migration of employed workers and employment in 75 regions in Western Germany over the period 1982-1997. Given a multinomial logit model for the individual migration decisions, we derive a conditional Poisson gravity model for the migration flows from one region to another. Although these migration flows are not observable, it appears that the in- and out-migration per region are sufficient statistics for maximum likelihood estimation, for each year separately. The correctness of the model specification is tested by the integrated conditional moment test on the basis of nonlinear regressions implied by the Poisson gravity model.