Multiproton transfer in which more than one proton is transferred, either synchronously or asynchronously, is an important phenomenon in chemistry and biology. The hydrogen bonds with a very low barrier, leading to proton delocalization in the H-bond, are called "short strong" or "low-barrier" hydrogen bonds (SSHB or LBHB). It has recently been proposed that they may provide an unusually large amount of stabilization to high-energy enzyme-bound intermediates and/or transition states. In order to study the role of such hydrogen bonds in the multiproton transfer, we have performed high-level ab initio quantum mechanical calculations for the potential energy surface of the formamidine-formic acid complex. The double-proton transfer occurs asynchronously with a strongly hydrogen bonded intermediate, and the barrier height is 3.95 kcal mol(-1), which is about 5-12 kcal mol(-1) lower than those of the concerted reactions in formamidine dimer and in formic acid dimer. The SSHB changes not only the barrier height but also the mechanism of the double-proton transfer. The strength of SSHB depends on environments. We have calculated the solvent effect at the HF and the B3LYP levels using the self-consistent isodensity polarized continuum model (SCIPCM). The strength of SSHB is reduced rapidly with increasing dielectric constants. It is about 29 kcal mol(-1) at epsilon = 10. The barrier height is also reduced with increasing dielectric constants, which indicates that the proton transfer becomes faster in a polar medium. These results suggest that the SSHB contribute to the proton transfer,greatly, and the energetics is changed very much with environment.