Bovine aortic endothelial cells (BAEC) were exposed to glucosylated albumin-gold complexes (GgA), and the distribution of the tracers was compared after cryofixation and after glutaraldehyde fixation. Morphometric analysis revealed differences in the GgA distribution depending upon the method of fixation used. In BAEC monolayers cryofixed after 3 min of incubation with GgA, tracer was observed in predominately apically located vesicular elements. After 16 min of incubation, all vesicular elements were labelled, and multivesicular bodies were the prominent labelled structure. In contrast, chemically fixed monolayers exhibited a heterogeneous distribution of GgA within vesicular profiles after 3 min and 16 min of GgA incubation. The differences in tracer distribution depending upon the fixation method must be resolved before the mechanism of vesicle-mediated endothelial cell transport function is defined and universally accepted.