The sequence encoding cre recombinase was under the control of the human beta-actin promoter. This line differs from other beta-actin driven transgenes in that expression was driven during early embryogenesis in a stochastic manner. While uniform transgenic expression was detected in the testis, mosaic patterns of cre-mediated recombination were observed in various organs including the liver, heart, lung, pancreas, brain, retina, spleen, and adrenal gland.