We present part of the results from a spectroscopic monitoring programme on a sample of AGNs, relative to Narrow Line Seyfert 1 Galaxies: following the idea that Balmer-line variability can help discriminate among the possible models for these objects, and on the basis of a first monitoring project with long time-scales, we now add to the previous database new variability results, both on short and long time-scales. The comparison with a similar data-set of normal Seyfert 1's suggests now a statistically different behaviour of NLS1s with regard to the 1-year variability properties, and a clearer trend of NLS1s towards weaker variability is suggested by the comparison between the 1-month variations of NLS1s and those of the typical Seyfert 1 NGC 5548. Although these results do not take into account the possible role of the relative contribution of narrow components to the line fluxes, and of the continuum variability amplitudes (both of which can in principle be different in the two classes of objects), they are consistent with the model of a BLR which is on average larger in NLS1s.