  Events with two or more leptons (electrons or muons) with high transverse
momentum are measured in electron-proton collisions at HERA using the data
sample collected in the period 1994-2005. Multi-lepton events at high
transverse momenta are of special interest as these signature might reveal new
physics beyond the Standard Model. An example is the single production of
doubly-charged Higgs bosons $H^{\pm \pm}_{L,R}$, which couple to leptons of the
$i^\prime$th and $j^\prime$th generation via Yukawa couplings $h^{L,R}_{ij}$.
Results from a search for doubly-charged Higgs bosons in the decays into
electrons, muons and taus are presented using data taken in the period
1994-2000. No evidence for doubly-charged Higgs production is found and we
derive limits on the $h_{ee}^{L,R}$ and $h_{e \mu}^{L,R}$ Yukawa couplings as a
function of the $H^{\pm\pm}_{L,R}$ mass.
