An analytical method has been developed for the separation of glyoxal (Go), methylglyoxal (MGo), and dimethylglyoxal (DMGo) by MEKC using stilbenediamine (SD) as derivatizing reagent, separation time 6.5 min, SDS as micellar medium at pH 8, and sodium tetraborate (0.1 M) as buffer. Uncoated fused-silica capillary, effective length 50 cm x 75 gm id; applied voltage 20 kV and photodiode array detection, were used. Calibration was linear within 0.02-150 mu g/mL with detection limits 3.5-5.8 ng/mL. Go and MGo, observed for diabetic and healthy volunteers, were within 0.098-0.193 mu g/mL Go and 0.106-0.245 mu g/mL MGo with RSD 1.6-3.5 and 1.7-3.4%, respectively, in diabetics against 0.016-0.046 mu g/mL Go and 0.021-0.066 mu g/mL MGo with RSDs 1.5-3.5 and 1.4-3.6%, respectively, in healthy volunteers. Go and MGo in diabetics were also measured by standard addition and DMGo as an internal standard. Additives do not contribute significantly to Go and MGo matrix.