The effect of plating solution constituents on the deposition rate and deposit composition of electroless Ni-based alloys (Ni-P, Ni-W-P, and Ni-Mo-P) was examined. Na2WO4 additions increase the deposition rate of Ni-P, whereas the addition of Na2MoO4 inhibits deposition. The addition of sodium gluconate to complex molybdate anions can reduce this inhibiting effect. The reactions involved in the electroless deposition of these alloys were investigated by cyclic voltammetry. Strong interactions between the cathodic and anodic processes occur. For Ni-Mo-P, introduction of Na2MoO4 into the Ni-P plating solution suppresses both the anodic and cathodic reactions, whereas addition of the Mo-gluconate complex facilitates the electrochemical processes. The different behavior of MoO42- and WO42- additions to Ni-P plating solutions can be explained in terms of the chemical species present at equilibrium in the two systems. (C) 2003 The Electrochemical Society. All rights reserved.