Non-enzymatic chemistry of glucose and L-ascorbic acid as precursors and α dicarbonyl intermediates are referred as Maillard Reaction and play an important role in vivo. α Dicarbonyl compounds lead to the formation of advanced glycation end products (AGEs). AGEs play a prominent role in various pathophysiologies. In the present Ph.D. thesis quantitation methods for the complete spectrum of α dicarbonyl and AGE compounds relevant in vivo were developed and applied in clinical trials with hemodialysis patients vs. healthy controls. Furthermore, a new class of lysine amide modifications (amide-AGEs) based on non-enzymatic Maillard mechanisms was established. N6 Hydroxyethyl lysine was introduced as a new marker for oxidative stress in vivo based on the redox-equilibrium formed by protein bound glycolaldehyde and the α-dicarbonyl compound glyoxal. In vitro experiments enlightened the mechanistic relationship of the redox partners. In addition, a novel and very effective alternative mechanism of N6 carboxymethyl lysine formation with glycolaldehyde-imine as a reactive precursor was unraveled.