TheCre/loxP transgenic system may be used to achieve temporally and/or spatially regulated gene deletion. The Mx1Cremouse expresses Cre recombinase under control of the IFN-inducibleMx1 promoter. Mx1Cre mice were crossed with a reporter strain (ROSA26tm1Sor) in which β-galactosidase activity is expressed only after Cre-mediated recombination to determine the cellular pattern of Cre-mediated genetic recombination in the kidney and other tissues. Widespread recombination was observed in vascular endothelium as well as in the liver and spleen. Recombination was restricted to subsets of stromal cells in uterus, duodenum, colon, aorta, and kidney. In the cortex, χ-galactosidase activity was detected in a subset of tubules and all glomerular cells, including endothelium, mesangium, and podocytes. No χ-galactosidase activity was detected in proximal tubules. Costaining of kidneys with segment-specific markers demonstrated induction of χ-galactosidase activity in collecting duct, with sporadic labeling of the thick ascending limb but no significant labeling of distal convoluted tubules. We conclude that Mx1-driven gene recombination is spatially as well as temporally restricted. The Mx1Cretransgene should prove a useful reagent to achieve temporally regulated recombination in endothelial, glomerular, and distal renal epithelia in mice.