A tamoxifen-inducible icre recombinase gene and FRT-flanked beta-lactamase gene were inserted into the ATG start site of the murine Tek gene located on a BAC. After Flpe-mediated excision of the beta-lactamase gene, the targeted BAC was injected into FVB/N oocytes. Cre expression was detected in endothelial cells of numerous organs after treatment with tamoxifen.