A mesoscopic evolution equation for the density of random walkers is derived under exclusive dynamics and an additional interaction between the walkers. In lowest order of a gradient expansion we get a nonlinear transport equation of Kardar-Parisi-Zhang type with transport coefficients depending on the density itself and on the ratio of interaction strength and temperature. In case of an attractive interaction an unstable behaviour can be observed. Furthermore, the dynamics is discussed using renormalization-group techniques.