High plasma levels of homogentisic acid in alkaptonuria can be a potentially fatal condition, due to the toxic effects of the homogentisic acid, melanin (soluble and deposited), its intermediates and reactive oxygen side products. Their toxicity increases when antioxidant mechanisms are overwhelmed, and their formation in blood causes haemolysis (Hegedus 2000). However, the relationship between high plasma HGA concentration and haemolysis is still questionable. Alkaptonuria patients develop arthritis and often suffer from other diseases too, including cardiovascular and kidney disease. Fatal alkaptonuria cases are infrequent, and death often results from kidney or cardiac complications. Heng et al. (2010) reported a case of a young patient with alkaptonuria suffering from severe renal failure who developed fatal metabolic acidosis and uncontrollable intravascular haemolysis, which may have been caused by rapid and extensive accumulation of HGA and subsequent accumulation of plasma soluble melanins. Decreased serum antioxidative activity has been reported in patients with chronic decreased kidney function. Despite administration of large doses of antioxidant agents and intensive kidney support, haemolysis led to the death of the patient.