  The transfer of polarization from a high-energy positron to a \lam hyperon
produced in semi-inclusive deep-inelastic scattering has been measured. The
data have been obtained by the HERMES experiment at DESY using the 27.6 GeV
longitudinally polarized positron beam of the HERA collider and unpolarized gas
targets internal to the positron (electron) storage ring. The longitudinal spin
transfer coefficient is found to be $\dll = 0.11 \pm 0.10 \mathrm{(stat)} \pm
0.03 \mathrm{(syst)}$ at an average fractional energy carried by the \lam
hyperon $<z >= 0.45$. The dependence of \dll on both the fractional energy $z$
and the fractional longitudinal momentum $x_F$ is presented.
