The viscoelastic properties of the polyphosphoryldimethylamides were investigated by the technique of stress relaxation as a function of the N to P ratio, and therewith of the chain length. From the great similarity of the shape of the curves to those of “normal” organic polymers, i.e., poly(methyl methacrylate) or polystyrene as a function of the molecular weight, from the broad distribution of relaxation times, as well as from the difficulty of preparing samples below the gel-point, it is concluded that the relaxation mechanism in the flow region is molecular flow, with bond interchange along the backbone either completely absent or present to only a minor extent.