Experimental infection of nine cattle with seven rinderpest virus strains of different pathogenicity resulted in significant variations of clinical signs, morphological lesions and distribution of viral antigen in tissues. The severity of clinical disease was correlated with the extent of tissue alterations and the amount of immunohistologically detectable viral antigen. Both mild and virulent strains of rinderpest share essentially the same tissue tropisms in vivo, i.e. epithelio- and lympho-tropism. However, rinderpest virus isolates of higher pathogenicity showed a more rapid and wider distribution with more extensive lesions than milder strains, which probably accounts for the higher mortality.