The spread of citrus canker, which is caused by Xanthomonas campestris pathovar citri, was studied in Argentina. Disease gradients were obtained by plotting the proportion of diseased trees in individual rows or subplots of grouped rows vs. distances from inoculum sources. The Gompertz transformation was used to linearize the gradients when plotted vs. log10 (distance). In the regression equation for the linearized disease gradients, the slope b ranged from -0.2 to -4.13. Incidence of disease increased faster near inoculum sources; thus, disese gradients became steeper with time. The increasing steepness of the gradients was evident 40 mo. after an inoculum source had been eradicated. Slope values were approximately the same for 4 scion-rootstock combinations at a given value of the Y-intercept (a). However, a and b increased slower in time on a resistant scion-resistant rootstock combination. Foci were detected by doublet analysis. Primary spread of canker resulted in a distribution of disease trees that was sparse, but with a gradient. Diseased trees were not aggregated in the early spread. The later secondary spread was limited, and the incidence of disease increased faster near the inoculum sources. Aggregation of diseased trees then occurred.