The metabolic fate of a herbicidal methylmercapto-s-triazine (cyanatryn) in the rat.

1. A major route of metabolism of the methylmercaptotriazine herbicide cyanatryn involves S-oxygenation. 2. The S-oxide reacts spontaneously with glutathione affording a conjugate, which is eliminated in the bile, and a mercapturic acid which is eliminated in the urine. 3. A small proportion of the administered dose was covalently bound to a component of the blood, probably haemoglobin. This was shown to be dependent on the formation of the S-oxide and on the species of animal studied. 4. No reactivity of the S-oxide towards DNA in vivo or in vitro could be demonstrated.