A binomial sampling method for the potato aphid, Macrosiphum euphorbiae (Thomas), on processing tomato plants, Lycopersicon esculentum (Mill), is proposed. Relationships between mean number of M. euphorbiae per leaf and proportion of leaves infested [P(I)] with M. euphorbiae for both upper and interior leaves of the processing tomato varieties ‘Alta’ and ‘Halley’ are presented. A split-plot design was used with variety, position in the plant canopy, and block as the factors examined through linear regression and analysis of variance (ANOVA). Results supported the hypotheses that M. euphorbiae densities on upper canopy leaves are predictive of densities on inner canopy leaves and that proportion of M. euphorbiae infested leaves are predictive of mean densities per leaf. Mean M. euphorbiae density was greater on ‘Alta’ than ‘Halley’ tomato plants, supporting the assumption that ‘Alta’ is the more susceptible variety. Taylor’s Power Law coefficients, a and b, were similar for proportion of M. euphorbiae–infested upper and inner leaves of both ‘Alta’ and ‘Halley’. Taylor’s b coefficients ranged from 1.57 to 1.74, indicating a highly clumped distribution for M. euphorbiae.