An explanation has been advanced for the previously reported observation that alkaline hydrolysis of humic acids will release amino acids that are resistant to acid hydrolysis. It is thought that under the alkaline conditions oxidation of N-phenyl-amino acids to the more readily hydrolysed quinonimines occurs. The importance of oxidation in this step has been demonstrated by showing that acid hydrolysis in the presence of hydrogen peroxide will release amino acids that are stable to non-oxidative acid hydrolysis.