A 40 kb genomic fragment of Fev enhancer sequence and a beta-globin minimal promoter drive expression a fusion gene of cre and a mutant human estrogen receptor. This transgene also contains beta-globin intron and simian virus 40 polyadenylation sequences. After tamoxifen treatment this line shows recombination in up to 80% of the serotonergic neurons in the dorsal Raphe nucleus (B6, B7) the medial Raphe nucleus (B5, B8) and B9 nucleus. Minimal recombination is seen in the medullary nuclei (B1-B3).