The polymerization of 1,3-butadiene (Bd) in a stirred batch reactor with the ternary catalytic system Nd(versatate)(3)/Al2Et3Cl3/Al(i-Bu)(2)H in cyclohexane at 70 degrees C has been studied with initial emphasis on the effects of the order of addition of the catalyst components, the concentrations of Al2Et3Cl3 and Al(i-Bu)(2)H. Using in situ catalyst activation, the optimum concentration ratios of Nd(versatate)(3)/ Al2Et3Cl3/Al(i-Bu)(2)H = 1:1:25 at a catalyst concentration of 0.11 mmol Nd/100 g Bd was established and used to determine the influence of water and excess versatic acid ([versatic acid]/[Nd]-3) on polymerization performance. It was found that the optimum catalyst characteristics were obtained when [H2O][Nd] = 0.11; higher and lower amounts of water decreased conversion, broadened the molecular weight distribution and increased the molecular weight. Increasing the level of excess versatic acid above [excess versatic acid/Nd] = 0.22 resulted in lower conversions, broader molecular weight distributions and higher molecular weights. Polybutadiene cis-1,4 contents were consistently high for all polymerizations (ca. 98%) and were found to be independent of the water content and excess acid level.