SUMMARY An avirulent strain KH 3 J of M. mycoides was shown to make a good immunizing agent in Zebu cattle in Nigeria when administered as a broth culture vaccine. The same strain in the form of lyophilized broth culture vaccine was also satisfactory if there was an adequate number of viable organisms per dose. It was found that animals when challenged one year after vaccination with the lyophilized product were still immune. The value of agar agar as an adjuvant was investigated.