With incoherent quasielastic neutron scattering self-diffusion coefficients in pure iron, and iron-carbon alloys containing 8.7 at% and 16.9 at% carbon have been measured. At the melting point in liquid iron is m2 s−1. For the close-to-eutectic Fe83.1C16.9 composition m2 s−1 at T K. Contradicting conclusions drawn from literature values of tracer diffusion experiments the addition of carbon has only a minor effect on the iron mobility: at a given temperature the self-diffusion coefficient in Fe83.1C16.9 is only 10% larger than in liquid iron, although mixing has a drastic effect on liquidus temperature and phase behavior.