Glial fibrillary acidic protein (GFAP) is the major intermediate filament protein in the mature astrocytes. We have assayed for the presence of GFAP mRNA gene in mouse tissues outside the nervous system. Nuclease S1 protection experiments show that RNAs lacking exon 1 are transcribed in bone marrow. From a mouse bone marrow cDNA library we isolated GFAP cDNAs which start in the 3′ part of intron 1 and contain all the dowstream GFAP exons. The new GFAP mRNAs, which we call GFAPγ mRNAs, are already present in the brain at embryonic day 15 and in adult forebrain and cerebellum. Their presence in astrocytec cell lines suggests that astrocytes may be the site of in vivo expression of these mRNAs. In addition we have detected GFAPγ mRNAs in mouse spleen. Futhermore in human an analogous GFAP mRNA containing the 3′ part of intron 1 and lacking the exon 1 is also present in adult brain. These results suggest a new regulation of the GFAP gene expression. © 1995.