Soil redox potentials are relative indicators of aeration. This study was conducted to monitor redox potentials throughout the growing season in a continuous tillage-continuous maize (Zea maysL.) field study and to determine if redox potentials reflected differences in tillage treatment. Platinized electrodes and salt bridges were installed at depths of 15, 30, and 45 cm in four replicates of no-tillage (NT), moldboard-plow (MP), chisel-plow (CH), and ridge-tillage (RT) treatments on a Tara silt loam soil (Pachic Udic Haploboroll) and monitored during the growing season. Locally weighted regression and repeated measures analysis of variance were applied to the data. Tillage affected aeration of each soil depth zone at different times during the growing season. Mean redox potential measurements ranged from about 400 to 650 mV at the 15-cm depth; only redox potentials in NT and CH treatments were depressed to 250 to 300 mV in early 1985 (after an exceptionally wet October in 1984). At the 30-cm depth, mean redox potentials ranged from about 250 to nearly 700 mV; potentials in RT and NT treatments ranged from about 400 to >650 mV throughout both growing seasons. Changes of more than ±200 mV were observed at the 450-mm depth and appeared only partially related to water content, except in late 1986 when mean potentials of all treatments declined by >100 mV. Ridge-tillage treatments tended to maintain greater redox potentials and undergo less change at the 15− and 30-cm depths than other tillage treatments. Tillage affected redox potentials below the tilled zone, and MP treatments appeared least aerated at the 45-cm depth relative to other tillage treatments.