Oxalyl thiolesters and N-oxalylcysteine are normal mammalian metabolites.

A method for the quantitative analysis of N-oxalylcysteine and oxalyl thiolesters (RSCOCOO-) in biological samples is described. These compounds were found in all rat tissues examined (kidney, liver, brain, heart, muscle and fat), with the amount of N-oxalylcysteine ranging up to 18 nmoles/g wet weight and that of oxalyl thiolesters up to 65 nmoles/g wet weight. The identification of such compounds in animal tissues adds further credence to the hypothesis that they may be important metabolic effectors.