Output-only modal analysis allows the estimation of modal models for structures in their real in-operation conditions. One of the main drawbacks of this approach is that a part of the modal model can no longer be estimated. As a result, the operational mode shape estimates remain incorrectly scaled, dependent on the unknown level of ambient excitation. This incompleteness somewhat restricts the applicability of in-operation modal models. No techniques were previously available for the normalisation of operational mode shapes purely based on experimental output-only data. Recently, a sensitivity-based normalisation approach, that can be used for output-only data, was proposed and successfully tested on simple laboratory structures. The principle behind the normalisation technique is the interpretation of the shifts in modal parameters induced by well-known structural modifications. In this contribution, the sensitivity-based normalisation approach was experimentally validated on a basis of vibration experiments performed on a tractor-sprayer combination. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Science Ltd.