Alternating currents were delivered to lactating cattle through the milk during milking. Electrodes were placed at the top of each short milk tube and jointed for one electrical contact. A metal grid on which the cows' rear hooves stood during milking was the second contact. Constant voltages (0 to 16 V) applied to contacts showed first lactation cows to be more sensitive than multiple lactation cows. First lactation cows kicked milking machines at 8 V (currents greater than 5 mA), and multiple lactation cows kicked at 16 V (currents greater than 8 mA). At lower voltages, there were no consistent significant differences in milking duration, milk yield, or composition for primary or residual milk. Application of constant currents of 5 mA for first lactation cows and 8 mA for multiple lactation cows produced no undesired behaviors but did result in some differences in production variables. Milking duration decreased during application of constant current to first lactation cows. Blood cortisol monitored in the multiple lactation cows during trial 2 showed a significant increase during milking but was equivalent or less during application of current. This study demonstrates that currents of 5 mA or less, delivered through the milk line, did not produce any direct economic effect. To produce this current, voltages on the milk pipe line would have to be in excess of 125 V (obvious human safety hazard) or in excess of 5 V on the claw of the milking cluster.