Three parts of the brain, cerebral cortex, lining of ventricle and choroid plexus, are cleared of trypanosomes to different extents by different drugs. There appear to be several barriers preventing drugs from acting in different parts of the brain, the concept of a single "blood-brain barrier" does not account for the phenomena observed. The protection of trypanosomes from certain drugs by the choroid plexus and ventricular wall supports the concept of an intracellular stage of Trypanosoma brucei in the ependymal cell; this concept is also supported by differences in parasitaemia resulting from the inoculation of ependymal and of other tissues. Alternative therapies for sleeping sickness are suggested, one of which (suramin/metronidazole) is being advanced for trials in man.