We propose to observe the CfA sample of Seyfert galaxies in order to complete an earlier programme (CFA_AGN, Rodriguez Espinosa et al.) succesfully carried out so far. Prior ISO observations have revealed two different components in the mid to far IR spectral energy distribution of AGN (Rodriguez Espinosa et al., A&A 1996, Accepted). The new observations with ISO will not only complete the sample allowing unbiased statistical results for the whole class of Seyfert galaxies, but also will unambiguously define the mid-IR range, which after the first ISO data has become a test ground for the understanding of the AGN phenomenon. The new observations will also be aimed at solving the question of determining the size of the emitting region for each of the two components mentioned above. Thus, the major goals of this new proposal are: 1) To characterize the spectral energy distibution of AGNs, and in particular to confirm the bimodal dust emitting regime seen in most of the objects of the CfA sample observed with ISO so far. 2) To determine the origin of the mid to far IR emission in AGNs, and in particular to address the problem of whether this emission is compact or on the contrary rather extended. 3) To produce quantitative results on the fraction of energy originating in the active nucleus versus that originating in star forming regions. 4) To probe the differences between Seyfert type 1 and 2s in relation with the unified models and the possible existence of a dusty torus hiding the nucleus in the type 2 Seyferts.