Brains from young (20 day old) and adult rats were used to compare myelin yields obtained by sedimentation and flotation techniques. The flotation method consistently gave approx 70% higher yields of myelin than the sedimentation method. Both myelin preparations have virtually identical protein composition as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Electrophoretic analysis revealed substantial concentrations of myelin proteins in the non-myelin particulate fraction obtained by the sedimentation but not by the flotation method. The study indicates that the paradigm of the sedimentation method results in a significant loss of myelin during isolation, and that this loss can be avoided or minimized by employing the flotation method.