Mixtures of 13 normal and modified nucleosides in a 70 mM phosphate buffer solution (pH 6.7) supplemented with 100 mM of sodium dodecyl sulfate were separated by micellar electrokinetic chromatography in 25 min. Electrophoretic profiles of urine are obtained; it is demonstrated that 1-methylinosine and 1-methylguanosine nucleosides can be used as markers of precancerous states (mastopathy) and benign tumors (fibroadenoma).