AGID test is commonly used in the detection of ovine Paratuberculosis. This test detects the humoral immune response of the animals. However, its limitations are well know, due to its low sensitivity, related to the lesional type that the animal shows. Gamma-Interferon (-IFN) test could eliminate these disadvantages since it is based on the detection of the cellular immune response. In order to clarify these aspects, both tests were evaluated in lambs infected with Mycobacterium avium sbsp. silvaticum (Group A) and Mycobacterium avium subsp. paratuberculosis (Group Z). Samples of serum and blood were taken at different periods post-infection (50, 80, 120, 150, 220, 350 and 500 d.p.i.). Moreover, lambs from both groups were killed at 60, 120, 220 and 500 d.p.i. in order to evaluate the lesions and their correlation with the response in these immunological tests. -IFN test was useful to detect initial phases of the infection, showing positivity from the first day of testing in animals from both groups. This positivity was clearer in group A until the end of the experiment. With respect to AGID test results, animals from group A were positive from the first day of testing, reaching 100% of positivity at 350 d.p.i., while in group Z, positive animals were seen only sporadically and from 120 d.p.i. One of the most important findings was the relationship between the response to AGID and -IFN test and the lesions in group Z. The presence of severe diffuse granulomatous enteritis observed in some animals at the end of the experiment, was related with both positivity to AGID and absence of response to -IFN test. In conclusion, both techniques could be used together because of their complementarity in the diagnosis of ovine paratuberculosis.