Electronic Journal of Differential Equations, Vol. 2009(2009), No. 106, pp. 1-10. Title: Strong monotonicity for analytic ordinary differential equations Authors: Sebastian Walcher (RWTH Aachen, Germany) Christian Zanders (RWTH Aachen, Germany) Abstract: We present a necessary and sufficient criterion for the flow of an analytic ordinary differential equation to be strongly monotone; equivalently, strongly order-preserving. The criterion is given in terms of the reducibility set of the derivative of the right-hand side. Some applications to systems relevant in biology and ecology, including nonlinear compartmental systems, are discussed. Submitted August 21, 2009. Published September 01, 2009. Math Subject Classifications: 37C65, 37C25, 92C45, 34A12. Key Words: Monotone dynamical system; limit set; irreducible; compartmental model.