In the present work, a comparative study of non-additive sputtering of secondary positive ions from light and heavy targets bombarded by light atomic and molecular projectiles has been studied. It was discovered that, as compared with a light target, non-additive sputtering of a heavy target is increased strongly when the light molecular ions are used as projectiles. The increase of non-additive sputtering is explained by an effect of the back-scattered projectiles who transfer additional energy into the subsurface layers of the target. (C) 2002 Elsevier Science B.V. All rights reserved.