  We predict a nonvanishing baryon asymmetry of the proton sea at low $x$. It
is expected to be about $7\%$ and nearly $x$-independent at $x < 0.5 \times
10^{-3}$. The asymmetry arises from the baryon-antibaryon component of the
Pomeron, rather than from the valence quarks of the proton, which are wide
believed carriers of baryon number. Experimental study of $x$-distribution of
the baryon asymmetry of the proton sea can be performed in $ep$ or $\gamma p$
interactions at HERA, where $x\sim 10^{-5}$ are reachable, smaller than at any
of existing or planned proton colliders.
