A study was carried out to determine if electromagnetic fields of high voltage transmission lines can interfere with electromagnetically guided cornering systems associated with some center pivot irrigation units. Using electromagnetic susceptibility tests, it was found that 60 hertz magnetic fields of more than approximately 500 mG (milligauss) are required to cause interference with the operation of one system. This level is significantly higher than those found near most high voltage transmission lines. It was also found that the magnetic fields at harmonic frequencies and wideband fields due to corona on the transmission line studied were insufficient to cause interference with cornering guidance systems. Observations of center pivot cornering systems operating properly near 345 kV transmission lines in Nebraska, USA, confirmed these results.