In a previous study, spiroarsoranes were very effective against both the two pathogenic phases of the experimental sheep trypanosomiasis. In this paper, the authors had studied the plasmatic pharmacokinetics of these compounds. Data had shown one peak 10 min after injection of a 3 months inoculated sheep, and 90 min for the control sheep. Spiroarsorane had a good diffusion into the central nervous system, but the trypanocidal activity, during the second phase of the disease, was effective only after repeated treatment. The spiroarsorane low toxicity could allow its direction against nervous trypanosomiasis.