This paper is a contribution to the understanding of the interaction between overall lateral-torsional buckling and local buckling of a beam under transverse loading. It concentrates on the case where the critical load for local buckling is smallest. Three approaches have been used: numerical analysis using the asymptotic theory; a qualitative analysis using an a priori simple discrete model; and experiments. The study suggests that just three modes in the asymptotic analysis are adequate to describe the interactive behaviour. The resulting reduced potential energy expression is quite similar to that of the a priori simple discrete model and provides insight into the destabilizing phenomenon. The experiments confirm these results.