The ability of the African trypanosomes to vary their surface coats of glycoprotein antigens during infections of susceptible host animals has prevented the development of vaccines employing cell surface proteins, as is being attempted with other parasitic protozoa (see Cohen, 1986). Since the phenomenon of antigenic variation in protozoa was the subject of another symposium, of the five papers presented in this symposium one dealt with the possibility of sexual phenomena occurring in trypanosomes, one with the transmission of the organisms by tsetse to vertebrate hosts and one with the characteristics of the trypanosomes isolated from man. The fourth paper described the vertebrate host response to the parasites and the fifth described the control of such infections by chemotherapy.