Abstract The results of a detailed study of isothermal grain growth in zone-refined iron in the temperature range 550 to 850°C are presented. The empirical growth law, D = Ktn, is obeyed and the time exponent, n, increases with temperature, from approximately 1/4 to 1/2. Correspondingly, the driving-force exponent, m, in the rate equation for boundary migration, V = M(∆F)m, varies from 3 to 1. Within the temperature range studied, grain-growth kinetics cannot be represented by a single thermally activated process; the boundary motion appears to be impurity-controlled. The grain size and shape distributions are not log-normal and are practically invariant during normal grain growth. These results are discussed and compared with recent grain-growth theories. Resume L'auteur presente les resultats d'une etude approfondie de la croissance isotherme du grain dans le fer de zone fondue pour un intervalle de temperature de 550 a 850°C. La loi empirique de croissance, D = Ktn, est verifiee et l'exposant n augment...