Bovine trypanosomosis is a serious constraint to livestock development in large parts of Mozambique. In most areas where tsetse flies are present, the disease in livestock is controlled using curative and prophylactic trypanocidal drugs. Those drugs have been used for many years and new drugs are unlikely to become available in the near future. As a result, trypanosomes have developed resistance against the currently available trypanocidal compounds. Drug resistance has been detected in various African countries and is a serious impediment to the control of livestock trypanosomosis. A study was initiated to determine whether drug resistant trypanosome strains are present in Zambézia Province of Mozambique. The aim of this study was to determine the sensitivity of Trypanosoma congolense isolates from Chinde, Nicoadala and Maganja da Costa Districts to diminazene aceturate, isometamidium chloride and homidium chloride. To assess the effect of the farming system and the intensity of drug regimens on the development of drug resistance, trypanosome isolates were collected from cattle from subsistence, semisubsistence and commercial livestock production systems. Drug-use practices in each of the production systems were determined using a questionnaire. The methodology used to assess the level of drugs resistance in the trypanosome isolates was the standardized method described by Eisler et al. (2001). Seven isolates were selected for resistance testing. For each of the seven isolates, five different doses varying between 0.01-20 mg/kg body weight for isometamidium chloride, 0.01-10 mg/kg body weight for homidium chloride and 1-30 mg/kg body weight for diminazene aceturate were used. For each dose rate six mice were treated intraperitoneally with the appropriate quantity of the drug dissolved in 0.2 ml of sterile distilled water 24 hours after the inoculation of the blood containing the trypanosomes. The control mice (six mice per trypanocidal drug) received the same amount of water without the drug. In four of the seven isolates high levels of multiple drug resistance (diminazene aceturate and isometamidium chloride) were detected. One isolate had a low level of multiple (diminazene aceturate and isometamidium chloride) drug resistance. Two isolates were susceptible to both diminazene aceturate and isometamidium chloride. One of those was highly susceptible to isometamidium chloride even at the lowest dose rate. The observed levels of drug resistance could in most cases be correlated to the drug-use practices in the particular livestock production system. The results obtained from homidium chloride treatment are not conclusive, because most the mice cured after receiving 10 mg/kg body weight of the drug. Hence more research is required to establish the homidium threshold in mice. The results of this study should be useful to define the strategy of disease control in places where resistance of trypanocide were been reported. / Dissertation (MSc (Veterinary Science))--University of Pretoria, 2005. / Veterinary Tropical Diseases / unrestricted