A number of peculiar aspects characteristic of trypanosomes, protozoan haemoflagellates belonging to the order Kinetoplastida, which are not present in other eukaryotic organisms are reviewed. These aspects include: properties of the cytochromes and glycerol-3-phosphate oxidase; the structure of kinetoplast DNA; a mini-exon sequence present in messenger RNAs; naturally occuring chloramphenicol resistance; the presence of a peculiar cyclic AMP binding protein; a novel glutathione reductase and glycosomes. The latter are microbody-like organelles containing enzymes of glycolysis. carbon-dioxide fixation. de novo pyrimidine biosynthesis and purine salvage.