Expression of the CD44 molecule was examined in a variety of human brain tumours, brain metastases and normal brain. Immunohistological staining with several CD44 antibodies demonstrated differential expression of the CD44 molecule among different brain tumour types. CD44 was strongly expressed in high-grade gliomas and weakly expressed in meningiomas, medulloblastomas and normal brain. Northern blot analysis revealed the presence of 3 major CD44 mRNAs of 1.6, 2.2, and 5.0 kb in glioblastomas and a mRNA of 5.6 kb in meningiomas. CD44 expression was also detected by flow cytometric analysis on cultured cells derived from a variety of human brain tumours including glioblastomas and meningiomas.