Results of preclinical assay, preparation and conservation of a S.-dublin live vaccine based on streptomycin dependent mutants and for oral application are demonstrated and discussed in detail. The used oral vaccine is very good tolerated by calves and results in stable immunity after administration of a daily dose of 5 x 10(10) bis 1 x 10(11) living Smd.-mutants for 10 consecutive days. Complete immunity developes in calves within a period of two weeks after the last antigen administration and persists up to the age of 5 to 6 months. Conserving the vaccine at low temperatures (-15 degrees C) the number of living organism is far-reaching preserved in the first 5 months after preparation. After thawing the vaccine is to be used within a period of 3 days. With respect to the preparation of the live vaccine on semisynthetic nutritiv media some informations are given concerning the improvement of bacterial yield.