Experimental observations suggest that type 1 and type 2 astrocytes have distinct lineages distinguished, respectively, by the absence or presence of the A2B5 antigen. To investigate the hypothesis that the strikingly different biological behaviors of low-grade and high-grade astrocytomas might be related to cell lineage, 38 astrocytomas (grades I through IV), were examined for the presence of the A2B5 antigen, glial fibrillary acidic protein (GFAP), and galactocerebroside (GC), a marker for oligodendrocytes. Twenty-nine of the tumors (76%) were composed of moderate or high densities of GFAP+ and unlabeled cells, and were devoid of A2B5+ and GC+ neoplastic cells. Only four tumors had high densities (75% to 100%) of A2B5+ cells, three of which were grade I tumors; two tumors, also Grade I, contained moderate densities (20% to 25%) of GC+ cells that had cytologic features of astrocytoma or oligodendroglioma. The findings suggest that most cerebral astrocytomas lack the A2B5 antigen and thus may represent neoplasia along the type 1 astrocyte lineage. In contrast, A2B5+ lineage among astrocytomas, ie, neoplasia with differentiation toward type 2 astrocytes and GC+ oligodendrocytes, is less common and may be correlated with prognostically favorable histopathologic features.