Illimaquinone, a sponge metabolite that disrupts the Golgi complex in mammalian cells, stopped proliferation and induced morphological and ultrastructural changes in promastigotes of L. mexicana Radioactive labeling of proteins demonstrates an increased excretion function and diminution of membrane acid phosphatase activity, due probably to the vesiculation of the Golgi complex and alteration of the cell protein sorting mechanism. The result indicated that illimaquinone could be useful for the study of intracellular traffic in Trypanosomatidae.