  We investigate the basis properties of sequences of Fucik eigenfunctions of
the one-dimensional Neumann Laplacian. We show that any such sequence is
complete in $L^2(0,\pi)$ and a Riesz basis in the subspace of functions with
zero mean. Moreover, we provide sufficient assumptions on Fucik eigenvalues
which guarantee that the corresponding Fucik eigenfunctions form a Riesz basis
in $L^2(0,\pi)$ and we explicitly describe the corresponding biorthogonal
system.
