Glioblastomas are highly invasive intracerebral tumors that are known to express the CD44 cell adhesion molecule. Human glioma cell adhesion and invasion in vitro may in part be mediated by the interaction of CD44 with extracellular matrix proteins. To suppress the growth and invasive effects of CD44 expression on primary brain tumors we have designed two hammerhead ribozymes as potential gene therapeutic agents. Both ribozymes designed to target exon 2 of CD44 exhibited in vitro cleavage of in vitro transcribed CD44s and CD44R1 RNAs. The anti-CD44 effect of these ribozymes results from directed RNA cleavage, requiring both a target sequence and an appropriate catalytic center. Further, following transient transfection of one of these ribozymes into the SNB-19 glioma cell line, significant in vivo cleavage activity against cellular CD44 transcripts was demonstrated by flow cytometrical analysis. These preliminary results suggest that CD44-directed hammerhead ribozymes may be useful as gene therapeutic agents.