Laminar fully developed flow and heat transfer have been analyzed for a duct in which there ore cross-sectional nonuniformities. The nonuniformity consists of a spanwise-periodic array of rectangular protuberances that extend into the flow cross section from an otherwise plane wall. The other bounding wall of the flow cross section is plane and smooth (no protuberances). To attain solutions with a minimum number of parameters, the general problem of heating at both walls is broken down into two subproblems, in each of which only one of the two walls is heated. Extensive numerical solutions were carried out for each of the subproblems, and the superposition procedure by which these results are used for the general problem is described. The finite-difference formulation was facilitated by the use of two-noded control volumes deployed adjacent to the boundaries of the solution domain.