The bacterial Cre recombinase gene was inserted into the first exon of an expression cassette (clone 445) that contains all the introns, promoter regulatory elements, exons, and 2.5 kb of 5' and 2 kb of 3' flanking DNA of the astroglia-specific mouse glial fibrillary acidic protein gene. GFAP is not expressed from the transgene due to deletion of part of exon 1. Cre expression was detected in a small population of cells within the subependymal zone in the adult brain. No Cre expression or activity was detected during embryonic development or in the hippocampus.