range of luminosities for which $\rm H\alpha$ E.W. and H band photometry are available. Following GPB96 we assume that the H band luminosity is proportional to the galaxy dynamical mass.

To discuss point ii), we compare the systematic (i.e. derived from a survey having the character of completeness) $\rm H\alpha$ properties of spiral galaxies as a function of some indicator of their environmental conditions, e.g. their local galaxy density or the projected radial distance from the cluster centers. To this purpose Kennicutt & Kent (1983, KK83 hereafter) carried out an $\rm H\alpha$ survey of galaxies belonging to the Virgo cluster and compared them with isolated objects. Kennicutt (1983b) tentatively concluded that galaxies belonging to the core of this cluster have a SFR significantly quenched in comparison to normal galaxies. Kennicutt, Bothun & Schommer (1984, KBS84 hereafter) extended this study to other dynamical entities, such as the Cancer cluster, Coma and A1367. The sample they collected, however, was not sufficient to derive general conclusions. Neither sufficiently complete was the $\rm H\alpha$ study by Gavazzi, Boselli & Kennicutt (1991, GBK91 hereafter) who carried out an aperture photometry, narrow band survey of another 55 late-type galaxies in the Coma ridge. They found that 