Abstract A method for the isolation of plasma membranes from an experimental murine ependymoblastoma is described. In this procedure, 5′-nucleotidase was used as the plasma membrane marker, since cytochemical methods demonstrated that the enzyme was present on this subcellular structure only. The final plasma membrane preparation showed a 15-fold enrichment in 5′-nucleotidase activity and a 17-fold enrichment in the activity of phosphodiesterase I, another plasma membrane marker. The specific activity of β-glucuronidase (lysosomal enzyme) was twice that of the whole homogenate, the specific activity of arylesterase (microsomal enzyme) was similar to that of the whole homogenate and succinate dehydrogenase (mitochondrial marker) was not detected. Electron microscopy of this fraction showed vesicles on which 5′-nucleotidase activity could be demonstrated. The subcellular distribution of [ 3H]amphotericin B per mg of protein was similar in the plasma membrane preparation and in the whole homogenate. It is concluded that, in ependymoblastoma, amphotericin B shows no selective affinity for the plasma membrane.