Selected paraffinic and naphthenic phytobland oils used as adjuvants markedly enhanced the foliar uptake and acropetal translocation of ring-labeled atrazine [2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine] by corn (Zea mays L. ‘VPI 646′), when compared with atrazine-14 C applied with nonionic polysorbate surfactant or in aqueous 25% methanol alone. Generally, 14C uptake increased with increasing concentration (1.25 to 20.0%) of a 100-sec viscosity paraffinic oil and with time (up to 32 hr) after application. No consistent additional promotion of atrazine-14 C uptake was derived from the use of emulsifier concentrations above 2.0% in the oil of a 10% oil-in-water emulsion. With a few exceptions, paraffinic and naphthenic oils of comparable viscosities were about equally effective as penetrant aids for atrazine. For both the paraffinic and naphthenic series, the 100-sec viscosity oils appeared to be slightly better penetrant aids than comparable 70, 150, and 200-sec oils.