Most cells in the retina and lateral geniculate nucleus (LGN) of primates have a concentric center/surround receptive-field organization. Details of the relationship between center and surround often can be used to predict how cells respond to visual stimuli. Models of the receptive-field organization and center/surround relationships also are useful when comparing cell classes. In the present study, we used the difference-of-Gaussians (DOG) model to quantitatively examine and compare the receptive-field center/surround organization of koniocellular (K), magnocellular (M), and parvocellular (P) LGN cells of owl monkeys. We obtained estimates of receptive-field center size (rc) and center sensitivity (Kc), and surround size (rs), and surround sensitivity (Ks) from 62 K, M, and P LGN cells by fitting their spatial-frequency responses with a DOG function (Rodieck, 1965; Croner & Kaplan, 1995). The DOG function not only accounted for the responses of P and M cells, but also provided a good description of K-cell responses. We found that at matched eccentricities of less than 15 deg, K cells had the largest rc and rs among the three cell classes. K cells also had the lowest Kc and Ks.