Let L = -Delta + V be a Schrodinger operator in R(d) and H(L)(1)(R(d)) be the Hardy type space associated to L. We investigate the bilinear operators T(+) and T(-) defined by T(+/-)(f, g)(x) = (T(1)f)(x)(T(2)g)(x) +/- (T(2)f)(x)(T(1)g)(x), where T(1) and T(2) are Calderon-Zygmund operators related to L. Under some general conditions, we prove that either T(+) or T(-) is bounded from L(p)(R(d)) x L(q) (R(d)) to H(L)(1)(R(d)) for 1 < p, q < infinity with 1/p + 1/q = 1. Several examples satisfying these conditions are given. We also give a counterexample for which the classical Hardy space estimate fails.
