The rupture strengths of individual asphaltene clusters in heptane-diluted bitumen were directly measured using a novel microcantilever technique. The majority of the ruptures occurred in the form of micron-sized fragments detaching from the original cluster (i.e. via 'surface erosion'). The average rupture strength of the clusters was found to be similar to0.4 muN. Within the resolution of the present technique, the strength of reflocculation (i.e. adhesive force between two already-separated flocs) was undetectable. (C) 2004 Elsevier Ltd. All rights reserved.