Field trials of two reduced doses of Brucella melitensis Rev 1 vaccine were conducted in Portuguese Merino crossbred ewes. All ewes had been bred 73-100 days prior to vaccination. Doses of 106 and 107 Rev 1 live organisms were given subcutaneously in treatment groups of 43 ewes and 42 ewes respectively, with an additional 25 ewes maintained as non-vaccinated controls. Ewes were monitored for 20 weeks post-vaccination by clinical observation, vaginal culture to detect B. melitensis Rev 1 excretion, and repeated serologic testing by Rose Bengal, serum agglutination, Complement fixation, and rivanol tests. No difference in live lambing rates was observed between the two treatment groups or the control. No shedding of vaccine organism was detected in vaccinated ewes. Serologic reactions were stronger and persisted longer in the higher-dose treatment group. Titers fell rapidly in the vaccinated ewes, with only one ewe testing positive beyond the eighth week.