Parametric resonance in regular waves is discussed. A set of non-linear equations is employed to describe the coupling between heave-roll-pitch modes. Limits of stability are the main area of interest of the paper. The present paper explores the influence of third order nonlinearities as well as the relevance of coupling between the vertical modes and the roll motion in the limits of stability. The influence of initial conditions on the development of roll amplifications is investigated and the effect of coupled or uncoupled modelling of the roll motion is addressed. © 2007 - IOS Press and the authors. All right reserved.