We perform a systematic analysis of the D-brane charges associated with string theory realizations of d = 3 gauge theories, focusing on the examples of the N = 4 supersymmetric U (N ) × U (N + M ) Yang-Mills theory and the N = 3 supersymmetric U (N ) × U (N + M ) Yang-Mills-Chern-Simons theory. We use both the brane construction of these theories and their dual string theory backgrounds in the supergravity approximation. In the N = 4 case we generalize the previously known gravitational duals to arbitrary values of the gauge couplings, and present a precise mapping between the gravity and field theory parameters. In the N = 3 case, which (for some values of N and M ) flows to an N = 6 supersymmetric Chern-Simons-matter theory in the IR, we argue that the careful analysis of the charges leads to a shift in the value of the B 2 field in the IR solution by 1/2, in units where its periodicity is one, compared to previous claims. We also suggest that the N = 3 theories may exhibit, for some values of N and M , duality cascades similar to those of the Klebanov-Strassler theory.1 The minus sign is the result of the conventions used in this paper, summarized in appendix B.