Four herds of zebus from northern Cameroon totalling 136 animals were vaccinated subcutaneously with the following doses of Brucella abortus strain 19: 5 x 10(9) colony-forming units (CFU), 10(9) CFU, 5 x 10(8) CFU and 10(7) CFU. Twenty-eight days after vaccination, the following seroconversion rates were observed respectively: 97.4, 96.2 84.2 and 73.3%. Of the 52 animals which could be tested subsequently including 39 over one year old on the vaccination day, only one showed antibodies 6 months after vaccination. The cost price of the strain 19 vaccine produced at the Boklé National Veterinary Laboratory was estimated to be 65 F CFA at the 10(9) CFU dose and 1,740 F CFA at the 5 x 10(10) CFU dose usually recommended. The use of the Buck 19 strain in the medical prophylaxis of bovine brucellosis in northern Cameroon is discussed.