This article raises important critical questions about efforts to reconstruct the "sira" of 'Urwa ibn al-Zubayr using the methods of isnad criticism, particularly as recently proposed by Gregor Schoeler and Andreas Gorke. While al-Zuhri and occasionally other authorities of his generation can often be persuasively linked with the traditions in question, the reach back to 'Urwa is generally not convincing (and even less so, the occasional invocation of 'A'isha and claims of "authenticity"). The primary difficulty is that the data of the biographical traditions generally cannot meet the demanding requirements of common-link analysis: their networks of transmission usually are not dense enough to establish sufficiently meaningful patterns beyond the early second century. Moreover, the arguments for 'Urwa's authorship often require a great deal of optimism regarding the accuracy of certain isnads and an occasional willingness to accept hypothetically reconstructed lines of transmission or to overlook difficulties in the recorded patterns of transmission. Equally significant is the failure so far of this arduous method to reveal anything particularly "new" about the "historical Muhammad" that could not otherwise be determined using simpler approaches.