In this paper we deal with the on-line addition of multioperands for conventional, carry0-save (CS) and/or Signed- Digit (SD) numbers. We propose an on-line Full-Adder (olFA) as the key element to design trees of adders to deal with multioperands. We also consider mixed inputs (e.g. SD and CS) and how to obtain the output in any of these representations. We show that for dealing with on-line multioperands it is more efficient to work with on-line CS trees based on olFAs than with on-line SD tree based on on-line SD adders. Finally a novel olFA-based architecture is proposed to directly deal with SD numbers.