Procedures for electrotransformation have been adapted for three pathovars of Xanthomonas campestris : campestris, vesicatoria and manihotis. Three differently sized plasmids (51, 9.3 and 3.3 kb) at different concentrations (10, 30 and 50 ng/sample) and different field strengths (10, 12, 14 and 18 kV/cm) were used. The efficiency of transformation was dependent on the recipient strain and the plasmid introduced. In general, a field strength of 14 kV/cm as well as a concentration of 30 ng plasmid DNA/sample seemed to be adequate for most conditions. Only X, campestris pv. vesicatoria strain 479 required a higher field strength for better efficiency. The plasmid size was inversely related to the efficiency of transformation; up to 1.6 x 10(10), 5.3 x 10(7) and 3.7 x 10(5) transformants/mu g DNA were obtained using the pXG31 (3.3 kb), pUFR027 (9.3 kb) and RP4 (51 kb) plasmids, respectively.