The properties of human glia and glioma cells in culture are reviewed. Glia-like cells from non-neoplastic brain show all accepted hallmarks of normalcy: limited life span, low terminal cell density, strong density dependent inhibition of proliferation, diploidy and contact inhibition of membrane mobility. Twenty five glioma lines have been studied. They all showed infinite life span, increased terminal cell density, relaxed density dependent inhibition of proliferation, aneuploidy and deficient contact inhibition of membrane mobility. So far all attempts to explain these departures from normal on the basis of a single metabolic defect have failed. Instead, all tested lines have shown an individual mosaic of structural and/or metabolic abnormalities characteristic for each line. This was particulary well demonstrated in studies of the glycosaminoglykans. The possibility is discussed that a malignant phenotype can a rise and exist in an almost infinite number of ways. The essential feature may be the acquisition of infinite growth potential which will set the stage for multiplication of genetic variants with an ever increasing fitness for proliferation and spread.