The influence of a flat interface on the isotropic to nematic (I/N) phase transition was investigated for aqueous solutions of cylindrical micelles of polybutadiene-poly(ethylene oxide) block copolymers using specular neutron reflectivity. While the I/N transition in the bulk occurs at the solute volume fraction phi(N/I), we observed the formation of a condensed layer close to a silicon single-crystal interface at volume fractions of about phi(i) approximate to 0.85phi(I/N). The thickness of this layer does not vary if the solute fraction is changed, while its density increases drastically within a very narrow range of volume fractions. This observation is interpreted as the formation of a nematically ordered layer which is induced by the interface.