Efforts to understand the basic mechanisms of angiogenesis, that is, the formation of new blood vessels from existing vasculature, have been limited by the methods that are currently used to measure vessel growth. Although in vivo assays provide the best environment in which to track angiogenesis, inherent difficulties in obtaining reproducible data limit the power of this approach. Limitations include: environmental variations between experimental animals, induction of inflammatory responses by surgical methods, and labor-intensive blood vessel quantification procedures. A better assay would measure vessel growth in one animal at multiple time points and would focus on minimization of artifacts induced by experimental manipulation.