The entire human beta-glucuronidase gene with 1.6kb of 5'-flanking sequence and 3.8kb of 3'-flanking sequence was microinjected into C57BL/6J zygotes. Founder line 4 was subsequently propagated. Mice that are homozygous for this transgene and the Gusbmps allele have approximately 20-fold higher beta-glucuronidase enzyme activity than wildtype controls. Distribution of human enzyme activity throughout various tissues mimics the endogenous mouse enzyme activity pattern.