  We present an explicit construction of the factorization of Seiberg-Witten
curves for N=2 theory with fundamental flavors. We first rederive the exact
results for the case of complete factorization, and subsequently derive new
results for the case with breaking of gauge symmetry U(Nc) to U(N1)xU(N2). We
also show that integrality of periods is necessary and sufficient for
factorization in the case of general gauge symmetry breaking. Finally, we
briefly comment on the relevance of these results for the structure of N=1
vacua.
