An 8.5 kb promoter fragment of mouse Nefh, containing the 5' UTR and 40 bp of non-coding sequence of exon 1 ending before the start codon, was adjoined to sequence encoding cre recombinase with an SV40 nuclear localization signal. An SV40 polyadenylation signal was also included in the construct. Expression of cre recombinase is driven in neurons of the brain and spinal cord during late development (around E18.5). Line 12 is best described and is representative of the other lines.