Longitudinal polarization of $\Lambda$ and $\bar \Lambda$ hyperons in deep-inelastic scattering at COMPASS

The production of $\Lambda$ and $\bar \Lambda$ hyperons by polarized muons of 160 GeV/c on a polarized $^{6}$LiD target has been studied using the COMPASS spectrometer. First preliminary results on the longitudinal polarization of $\Lambda$ and $\bar \Lambda$ hyperons produced in the deep-inelastic scattering will be presented for 2002 data set.