The Universidad Complutense de Madrid survey is a long-term project with the aim of finding and analyzing star forming galaxies using the Hα line as the tracer for star formation processes. In order to obtain a representative and complete sample of the population detected, spectroscopic observations were carried out for the full sample of Hα emission-line galaxy (ELG) candidates of the UCM lists 1 and 2. The ELGs types most commonly found (47%) are intermediate to low-luminosity objects with a very intense star-formation region which dominates the optical energy output of the galaxy. This kind of ELGs is similar to the galaxy population detected in the blue objective-prism surveys. And what is more important, a second population (43%) of star-forming galaxies with low ionization or high extinction properties has been found. This ELGs group is detected neither in the blue (University of Michigan survey, Case survey) nor in other surveys (Kiso, IRAS, Markarian) using other selection techniques.