A magnetohydrodynamic model is constructed for a cylindrical jet embedded i
n an external uniform magnetic field. It is shown that, as in the force-fre
e case, the total electric current within the jet can be zero. The particle
energetics and the magnetic-field structure are determined in a self-consi
stent way; all jet parameters depend markedly on the physical conditions in
the external medium. In particular, we show that a region with subsonic fl
ow can exist in the central jet regions. In real relativistic jets, most of
the energy is transferred by the electromagnetic field only at a sufficien
tly large magnetization parameter sigma > 10(6). We also show that, in gene
ral, the well-known solution with a central core B-z = B-0/(1 + omega(2)/om
ega(c)(2)) cannot be realized in the presence of an external medium. (C) 20
00 MAIK "Nauka/Interperiodica".