Pulsed-field gradient NMR has been used to study the self-diffusion of
polyions and counterions in polyelectrolyte solutions. The concentrat
ion dependence indicates a transition between the concentrated and sem
idilute regimes. In both regimes the molecular weight dependence is ap
proximately M-1 and mixtures of different molecular weights show an in
teresting behaviour. Mixtures with M(omega)/M(n) < 1.3 behave as a sin
gle fraction.