  We present model independent constraints on the masses and couplings to
fermions of $B$ and $L$ conserving leptoquarks. Such vector or scalar particles
could have masses below 100 GeV and be produced at HERA; we list the generation
dependent bounds that can be calculated from rare lepton and meson decays,
meson-anti-meson mixing and various electroweak tests. PLEASE NOTE: this file
does not contain tables and figures, so is not very useful. Complete paper
available (by mail) from<EMAIL_ADDRESS>