TITLE: Asymptotic behaviour of the stability parameter for a family of singular-limit Hill's equation. AUTHORS: R. Martinez Dept. de Matematiques, Univ. Autonoma de Barcelona Barcelona, Catalunya, Spain E-mail:reginamb@mat.uab.cat A. Sama Dept. de Matematiques, Univ. Autonoma de Barcelona Barcelona, Catalunya, Spain E-mail:sama@mat.uab.cat ABSTRACT: Under some non degeneracy conditions we give asymptotic formulae for the stability parameter of a family of singular-limit Hill's equation which depends on three parameters. We use the blow up techniques. The main contribution of this paper concerns the study of the non degeneracy conditions. We give a geometrical interpretation of them, in terms of heteroclinic orbits for some related systems. In this way one can determine values of the parameters such that the non degeneracy conditions are satisfied. As a motivation and application we consider the vertical stability of homographic solutions in the three-body problem. Preprint submitted to J. Differential Equations, 21 December 2007 Published in J. Differential Equations, 245 (2008) 3869-3897