In this paper,we study the leader-following rendezvous and flocking problems for a class of second-order nonlinear multiagent systems,which contain both extal disturbances and plant uncertainties.What differs our problems from the conventional leader-following consensus problem is that we need to preserve the connectivity of the communication graph instead of assuming the connectivity of the communication graph.By integrating the adaptive control technique,the distributed observer method and the potential function method,the two problems are both solved.Finally,we apply our results to a group of van der Pol oscillators.