Surfactants are widely used to enhance the performance of foliar applied chemicals, but their effects on foliar uptake are not well understood. Various effects are possible: on spray retention, depending on the wettability of plant surfaces; on penetration, by increasing the area of contact with the leaf; by acting as a humectant, keeping the spray droplets moist for a long time; by improving stomatal penetration; by lowering the surface tension of the spray solution; by facilitating movement along cell walls after entry into the foliage; and by lowering interfacial tensions. Surfactants could also influence cuticular penetration by acting as cosolvents or solubilizing agents, or by affecting permeability. To elucidate the effects of surfactants on penetration across the cuticle, the initial and primary barrier to foliar uptake, we investigated this question in vitro, using isolated cuticles. In this chapter, we report results concerning the effects of an ethopropoxylated fatty amine (Armoblen 557®) on the penetration of 14C-glyphosate, N(phosphonomethyl)glycine, across isolated tomato (Lyco-persicon esculentum Mill. cv. Marmande) fruit cuticles used as a model of the plant cuticle.