The herbicide glyphosate was nitrosated by third-order kinetics to N-nitrosoglyphosate. The nitrosation at 25 degrees C was maximum at the reaction pH of 2.5 and had a pH-dependent rate constant of 2.43 M-2 sec-1. An activation energy of 9.5 kcal mole-1 also suggested that glyphosate is nitrosated very readily. Thiocyanate increased the rate 4.6 fold. The possibility of using these results to predict the formation of N-nitrosoglyphosate under normal agricultural practice is discussed.