The course of immune reactions of the manifold antigens of Mycoplasma mycoides subsp. mycoides small colony type (SC) was analysed in serum and bronchial lavage of cattle experimentally infected with the African strain Afadé and the European strain L2 using Western-blots and complement fixation. Western-blot analysis of total antigens of both strains with sera from animals infected with the homologous and heterologous strain revealed the common dominant immunogenic antigens with the molecular masses of 110, 95, 85, 80, 72, 62, 48 and 39 kDa. The sequential sampling of the blood and bronchial lavages before and after contact infections allowed us to identify the antigens of 85, 80, 72, 48 and 39 kDa as particularly early immunogens. The IgA Western blots of the bronchial lavages showed distinct, early and persistent reactions to the 110, 85, 80, 72, 48 and 45 kDa proteins. These proteins were the predominant lipoproteins as determined by [14C]palmitic acid labelling. Only relatively weak reactions of the bronchial lavages were detected with IgG. In general immune responses were significantly stronger in the animals infected with the African strain Afadé, which gave positive results two weeks after contact infection. In contrast, the animals infected with the European strain L2 induced much lower reactions with a delay of three months after contact infection. In one animal strain L2 caused no sero-conversion and no infection. The results indicate a difference in virulence between the African strain Afadé and the European strain L2.