The structure and functioning of the cytoskeleton is controlled and regulated by cytoskeleton-associated proteins. Fused to the green-fluorescent protein (GFP), these proteins can be used as tools to monitor changes in the organisation of the cytoskeleton in living cells and tissues in different organisms. Since the localisation of a specific cytoskeleton protein may indicate a particular function for the associated cytoskeletal element, studies of cytoskeleton-binding proteins fused to GFP may provide insight into the organisation and functioning of the cytoskeleton. In this article, we focused on two animal proteins, human T-plastin and bovine tau, and studied the distribution of their respective GFP fusions in animal COS cells, plant epidermal cells (Allium cepa), and yeast cells (Saccharomyces cerevisiae). Plastin-GFP localised preferentially to membrane ruffles, lamellipodia and focal adhesion points in COS cells, to the actin filament cytoskeleton within cytoplasmic strands in onion epidermal cells, and to cortical actin patches in yeast cells. Thus, in these 3 very different types of cells plastin-GFP associated with mobile structures in which there are high rates of actin turnover. Chemical fixation was found to drastically alter the distribution of plastin-GFP. Tau-GFP bound to microtubules in COS cells and onion epidermal cells but failed to bind to yeast microtubules. Thus, animal and plant microtubules appear to have a common tau binding site which is absent in yeast. We conclude that the study of the distribution patterns of microtubule- and actin-filament-binding proteins fused to GFP in heterologous systems should be a valuable tool in furthering our knowledge about cytoskeleton function in eukaryotic cells.