In the present study channel flow with the lower wall mounted with streamwise riblets is considered. The laminar flow state is computed and its stability is investigated by superimposing infinitesimal perturbations, which leads to a hydrodynamic stability problem in a complex geometry. Linear stability characteristics for riblets with several scalloped cross sections are computed. The computations show that at theprimaryinstabilitylevel the laminar flow in the presence of riblets is more unstable than channel flow with smooth walls. ©1996 American Institute of Physics.