Diabetes is a disease among several others that has been linked with the accumulation of carbonylated proteins in tissues. Carbonylation is an irreversible, non-enzymatic modification of proteins by carbonyls. In Diabetes, dicarbonyls are thought to be generated by the autoxidation of reducing sugars which react with proteins and eventually lead to the formation of advanced glycation end-products (AGEs). Carbonyl scavenging drugs containing thiol or amine functional groups have been suggested to act therapeutically in preventing protein carbonylation by trapping the dicarbonyls glyoxal and methylglyoxal to form non-toxic adducts. This study seeks to determine the mechanism by which carbonyl scavenging drugs prevent glyoxal toxicity in a cell-free system as well as in isolated rat hepatocytes. In a cell free system, the glyoxal trapping ability of the drugs was measured by following glyoxal disappearance using Girard's Reagent T. For the thiol-containing drugs, the order of effectiveness for glyoxal trapping was penicillamine>cysteine>N-acetyl-cysteine, whereas for the amine-containing drugs, the order of effectiveness for glyoxal trapping was aminoguanidine>>pyridoxamine>metformin. Furthermore, aminoguanidine, penicillamine and cysteine at concentrations equimolar to glyoxal prevented protein carbonylation. Other scavenging drugs such as pyridoxamine, hydralazine or metformin did not prevent glyoxal-induced cytotoxicity by trapping glyoxal, but instead prevented cytotoxicity by acting as a mitochondrial vitamin, lipid antioxidant or reactive oxygen species scavenger, respectively.