Analysis of extracts of the bloodstream forms of Trypanosoma brucei showed that both DNA polymerase-α and DNA polymerase-β activities were present. The detection of DNA polymerase-β in T. brucei demonstrates the presence of this enzyme in unicellular organisms. DNA polymerase-β is present also in Leishmania mexicana . The DNA polymerases in T. brucei are immunologically distinct from the host enzymes. The structural differences between the parasite and the host enzymes could be exploited for the development of agents to combat parasitic diseases.