The N-terminal arm of the lambda repressor is shown to be flexible in solution by one- and two-dimensional 1H NMR methods. In particular, the relaxation of Thr-2 is largely independent of macromolecular tumbling. The conformation of the operator-binding domain is not affected by the removal of the first three residues nor by a point mutation, Lys-4----Gln. These results support a proposed model of the lambda repressor-operator complex in which the N-terminal arm of the repressor is assumed to be flexible and to wrap around the operator double helix.