Field tolerance to glufosinate in hybrid corn varieties (non-GMOs) was evaluated at physiological and biochemical levels. The present experiment was conducted to provide information for the development of a glufosinate-tolerant corn variety through a conventional breeding program. The effect of glufosinate on the physiological response to crop injury, plant height, and fresh and dry weight was examined in 15 locally adapted corn varieties to this herbicide. The highest degree of tolerance was observed in the varieties Pacific 626 and Pacific 983, while the most susceptible variety was CP 989. CP 989 tended to accumulate ammonia more than Pacific 626 and 983; and the concentration of glufosinate resulting in a 50% increase in ammonia concentration in CP 989 was half that required for Pacific 626 and 983. These results indicate that the degree of ammonia accumulation might be related to the sensitivity of these corn varieties to glufosinate.