In lipid monolayers consisting of two phases, the competition between
line tension and electrostatic repulsion can give rise to a stripe pha
se. The stability of this phase with respect to small harmonic distort
ions is analyzed. It is shown that the stripe phase is just marginally
stable when the stripes are of equilibrium width. As soon as the stri
pes exceed this width, coupled long wavelength distortions are energet
ically favored. Intermediate results concerning the stability of a sin
gle edge and a single stripe are also presented.