The influence of a variety of substances on technically relevant parameters of a nickel electroplating electrolyte (Watts bath) has been investigated. Special attention has been paid to the throwing power (TP), as well as visual appearance, current efficiency and codeposition of foreign atoms. Systems reported in the literature (e.g., inorganic salts to increase conductivity or complexing agents to increase polarization) were compared with typical reducing agents normally used in electroless Ni deposition. The mechanism of TP improvement in the case of sodium hypophosphite and dimethylamine-borane has been examined with the electrochemical quartz crystal microbalance (EQCM). Using the EQCM it was shown that there is a synergistic effect between the electrochemical and electroless deposition process. In addition, the activation energy of the latter was determined from temperature dependent measurements.