Adult animals from a known negative and an infected herd were vaccinated with reduced-dose Brucella abortus strain 19 vaccine. Since some of these animals developed elevated post-vaccinal blood titres, it is suggested that, when adult vaccination is decided on, such herds should be bled and tested about 4 months after vaccination and thereafter at 2 month intervals. Reactions with complement fixation titres of 392 IU ml-1 or higher on the first test should be taken as positive. During the 2nd and 3rd tests, positive reactions should be taken as less than 98 IU ml-1 and 49 IU ml-1, respectively. After vaccination, an overkill of up to 5%, due to vaccination reactions could be expected. Positive cases might occur up to 9 months after vaccinating an infected herd. On farms selected for adult vaccination suitable calving facilities in isolation, largely facilitate eradication. Lochia samples for the early diagnosis of brucellosis should be collected. Adult vaccination with a reduced dose S 19 vaccine, should be practised on selected, problem herds only, where the owner is fully aware of the consequences of this procedure.