An SV40 intron, cre recombinase cDNA and an SV40 polyA cassette were inserted into a vector behind the Vav1 promoter. The construct was injected into pronuclei to generate transgenic mice. 2 lines, 1 and 8, resulted and both exhibited recombination in the majority of hematopoietic and endothelial cells but very little in other somatic cells. (J:81647)