The presence in urine of desmosine (DES) and isodesmosine (IDES), two crosslinked amino acids unique to the elastic fiber network, can be used as a specific indicator of degradation of mature elastin. Compared to methodologies so far available, the capillary electrophoretic technique reported here seems to be suitable and convenient for determining desmosines in urine of patients affected by chronic obstructive pulmonary disease (COPD). By using 35 mM sodium tetraborate pH 9.3 containing 65 mM SDS as the background electrolyte, the peaks of DES and IDES could be detected in hydrolyzed urine samples from controls and patients. Owing to the simultaneous determination of endogenous urinary creatinine used as appropriate internal standard, the amount of these amino acids could be accurately quantified. The results obtained were of the same order of magnitude as the data already reported in the literature for COPD patients. Thus micellar electrokinetic chromatography (MEKC) may be considered as a reliable technique for studying the turnover of the elastic fiber in clinical conditions.