To verify the hypothesis of a possible involvement of free radicals of oxygen in some aspects of chronic renal failure, authors have executed, by high resolution liquid chromatography (HPLC), the measurement of plasmatic malondialdehyde (MDA) in 15 patients with chronic renal failure undergoing haemodialysis and in 15 healthy control subjects. The two groups were comparable for sex and age. Statistical analysis of the two groups resulted significant (p < 0.05). These results are according to literature data and show a problem of oxidative metabolism in subjects with chronic renal failure undergoing haemodialysis also if it might be useful to investigate the question with wider enumeration of cases, to clarify better the clinical significance of these alterations and to point out eventual correlations.