ESCRT (Endosomal Sorting Complex Required for Transport) proteins are required for the sorting of biosynthetic and endocytic proteins at multivesicular bodies (MVBs). Here, I describe an assay to evaluate conservation of endosomal sorting functions of plant ESCRT proteins by trans-species complementation analysis. The assay is based on the imaging of a fluorescent biosynthetic MVB cargo, the carboxypeptidase S (CPS) fused to the green fluorescent protein GFP, in yeast ESCRT mutants expressing putative plant orthologues of the missing yeast ESCRT components.