a significant number of S+Irr galaxies projected onto the two clusters have surprisingly strong $\rm H\alpha$ emission. These include the blue galaxies found in the Coma cluster by Bothun & Dressler (1986). A problem affecting these early studies was the lack of a well defined zero point for their environmental comparison, i.e. the properties of isolated galaxies were not known with sufficient accuracy. With the aim of establishing the present high mass SFR of spiral galaxies in the Universe and of comparing these properties in environments that differ by an order of magnitude in local galaxy density we undertook the present $\rm H\alpha$ imaging survey. The Coma supercluster offers a unique test-bed for such systematic study since it contains a filament of galaxies at constant distance from us (the “Great Wall”), thus a volume limited sample can be extracted from a magnitude limited sample. Moreover the properties of galaxies in two rich clusters such as Coma and A1367 (with a density of about 3 galaxies $\rm Mpc^{-3}$ brighter than 15.7) can be compared with those of relatively isolated galaxies (environments with about 10% of the cluster density), lying in the bridge between the two clusters at a similar distance from 