-Total chemi-ionization cross-sections have been measured over the 15 to 1 500 eV energy interval for collisions of He 2 1S and 2 3S metastable atoms with Ne, H2, N2, O2 and CO, using a slow ion measurement technique. With molecular targets these measurements have shown a strong energy dependence for the total ionization cross-section without dissociation. In the case of dissociative ionization an energy threshold appears, dependent on the energy defect of the reaction.