Some fundamental difficulties in the construction of an Earth-like dynamo model and the role of hyperviscosity in attempting to overcome these difficulties are discussed. An Earth-like convection model influenced by an imposed toroidal magnetic field is investigated both with and without the effect of hyperviscosity. It is shown that hyperviscosity affects the dynamics of convection significantly; the effect is similar in some respects to that of a strong magnetic field. The effective Ekman number, a key parameter for an Earth-like dynamo model, is substantially increased when hyperviscosity is employed. ¿ 1997 American Geophysical Union