A mean field theory has been developed to elucidate the orientational behavior of rodlike molecules, with two distinct orientations in the model, tethered onto a patterned surface. The binodal phase diagram of grafted rods can be symmetric and asymmetric, depending on the interactions between rods. By applying an external field to responsive grafted rods, the asymmetric phase diagram can be transformed into a symmetric one. The critical point of the field-induced phase diagram is relevant to the rod-rod interactions. (c) 2006 Elsevier B.V. All rights reserved.