Relationship between molecular gas and stellar mass (in solar units) when the molecular gas mass is determined assuming a constant X_CO factor (a), left) or the luminosity-dependent X_CO factor given in Boselli et al. (2002) (b), right). Symbols are as in Fig. 1, with in addition big blue empty circles indicating mean values and standard deviations for Hi-deficient objects. The black solid line indicates the linear fit determined using all gas-rich galaxies, while the black dotted line that determined for Hi-deficient objects (black empty symbols).