Both in tuberculosis and in leprosy there is clear evidence that genetic factors influence the susceptibility to infection. In the case of paratuberculosis no quantitative research has been performed with regard to this subject although this knowledge may beneficial to control programs. We have analysed data, retrospectively, of a ten year (1984-1994) follow up study of the efficacy of vaccination against paratuberculosis in Dutch dairy cattle. Records of over 7000 animals from 20 different farms were processed using a standard polygenic model. Separate analyses were done on populations with significantly different prevalence dynamics in the 10 year period investigated as well as on vaccinated and non-vaccinated animals. A Bayesian analysis was performed to estimate the marginal posterior distribution of heritability by a Markov chain Monte Carlo algorithm, and flat priors were used for variance components. The results indicate that there is a small genetic influence on the susceptibility of cattle to become infected with M. paratuberculosis. Heritabilities ranged between 0.029 and 0.05, with genetic standard deviations between 0.068 and 0.086. These results appear to be typical for disease traits: significant genetic standard deviations, which indicate that there are interesting differences between animals, but with low heritability. Searching for genes responsible for these differences could be a next step, as traditional selection would be inefficient.