Magnetic hysteresis data from young mid-ocean ridge basalts include samples with saturation remanence to saturation magnetization (Mrs/Ms) ratios greater than 0.5, the theoretical limit for an assemblage of single domain grains with uniaxial anisotropy. Under the usual assumption of dominant uniaxial anisotropy, the narrow single domain grain size distribution implied by these high Mrs/Ms values is difficult to reconcile with petrographic and remanence data that suggest the presence of larger multidomain grains. Dominant cubic anistropy provides a plausible explanation for the high Mrs/Ms ratios, and if generally valid, requires reinterpretation of granulometric and domain state inferences made form hysteresis data. ¿ American Geophysical Union 1995