A total of 47 women with metabolic syndrome (MS) were examined with the fractional determination of porphyrins in urine (uroporphyrin and coproporphyrin) and feces (coproporphyrin and protoporphyrin) as well as their precursors (5-aminolevulinic acid and porphobilinogen). Disorders of porphyrin metabolism were documented in 29 (61.7%) women All patients had elevated levels of porphyrin precursors. Five women exhibited qualitative changes in the form of abnormal ratios of different porphyrin fractions(coproporphyrin/uroporphyrin < 1--0.8 ± 0.1 vs normal ratio 3.6 ± 0.4). 21 patients suffered quantitative changes in porphyrin metabolism in the form of manifold increase of porphyrin levels in urine and/or feces and formation of biochemical syndromes of secondary coproporphyrinuiria, symptomatic rise in porphyrin content in feces, and chronic latent hepatic porfiria. Disorders of porphyrin metabolism were associated with insulin resistance. Changes of porphyrin metabolism in MS extend the spectrum of concomitant disturbances and can be regarded as an additional criterion.