Abstract: The present invention provides improved viral vectors useful for the expression of genes at high levels in human cells. In particular, the present invention provides recombinant adeno-associated vectors (AAV) suitable for gene therapy. These vectors are capable of delivering nucleic acid containing constructs which result in the production of full-length therapeutic levels of biologically active Factor VIII in the recipient individual in vivo. The present invention also provides pharmaceutical compositions comprising such AAV vectors, as well as methods for making and using these constructs.