Abstract
The collapse transition of a polymer chain on a two-dimensional lattice with directed bonds, the Manhattan lattice, is shown to occur at temperature Tθ=2ɛ/ln2, where ɛ is the attractive energy between nearest-neighbor pairs of monomers. The exact tricritical exponents are νt=(4/7 and γt=(6/7. The latter result differs from two recently proposed values of γt.