A transgenic construct containing the 1.3Kb enhancer and promoter sequence upstream of the of mouse homeo box B7 gene, a human growth factor mini gene and the Cre coding sequence was injected into fertilized C57BL/6 mouse eggs. Cre recombinase expression is detected in the mesonephric duct as early as embryonic day 9.5, in the ureteric bud by embryonic day 10.25 and in all ureteric bud epithelial cells by embryonic day 12.5. Low levels of expression are detected in the dorsal root ganglia and the spinal cord.