  We define the longitude Floer homology of a knot K in S^3 and show that it is
a topological invariant of K. Some basic properties of these homology groups
are derived. In particular, we show that they distinguish the genus of K. We
also make explicit computations for the (2,2n+1) torus knots. Finally a
correspondence between the longitude Floer homology of K and the Ozsvath-Szabo
Floer homology of its Whitehead double K_L is obtained.
