This presentation illustrates the use of (NP)-HPLC analysis to determine galactose incorporation into serum IgG, used as a biomarker for the improved monitoring and treatment of patients with Galactosaemia. Classical or severe Galactosaemia is a genetic condition caused by a lack of the enzyme Galactose-1-phosphate uridyltransferase (GALT), which normally breaks down galactose (the sugar found in milk and dairy products). This occurs in approximately 1:60,000 births annually in Europe but has a higher incidence in Ireland of 1:16,000 births where it is detected by newborn screening. Despite early treatment, the majority of affected patients worldwide go on to develop devastating long-term complications such as intellectual impairment, neurological complications, speech difficulties and infertility in females. These complications may be associated with abnormal synthesis of N-glycoproteins.