In this paper multi-stage ftow linPs with intermediate buffers are approximatt·d by two-stage line:; by u~:~ing repeated u.ggr<>gation. The aggregation nwthod uses restricted information of the output Jlattern of two-stage lines. The method is tested for the eaHe where all pt·oduetion units am unreliable with expmwntiallifeand repair-time~:~. It appeat·s that it performs well for most eases, provided we aggregate in t.he eotTeet sequenee.