Adults, infective larvae and microfilariae of Brugia malayi have been examined in the scanning electron microscope. In adult males the long spicule is solid with a spatulate anterior end. The small spicule is hollow and has a cup-like structure at the distal end which is covered by a hood. The infective larvae have dome-shaped caudal papillae, each with a gutter-like structure surrounding its base. The microfilariae are annulated with a distinct tail and a conspicuous hook at the cephalic end. These studies show that scanning electron microscopy of filariids can reveal features useful not only for distinguishing between species but also for understanding the functions of various organelles.