Vaccination has been widely used for the control of paratuberculosis. Traditionally, immunisation has been practiced during the first weeks of life under the hypothesis that infection takes place soon after birth. However, it has been demonstrated that vaccination does not prevent infection but modifies the host responses towards a limitation in the progression of lesions. Additionally, there are some evidences in tuberculosis suggesting that vaccination gives better results when it is carried out in animals around 5-6 months old. In this study, the cellular and humoral immune responses have been evaluated by means of gamma-IFN and ELISA tests respectively. Cell populations in circulating blood were studied by FACS analysis. Three flocks of sheep and three of goats have been used. In every flock, two groups of animals were made according to the age of vaccination (10-15 days and 4-5 months). Every group was composed of 15 animals each, in which 10 were vaccinated with a killed vaccine (Gudair(r)) and 5 kept as control. Both groups of animals showed a similar kinetics in the production of antibodies and gamma-IFN; however these responses appeared before, reached higher values and lasted for longer periods of time in animals vaccinated at 4-5 months than in younger animals.