We have measured serum total sialic acid (TSA) and lipid associated sialic acid (LSA) concentrations in 75 patients with non-insulin dependent diabetes mellitus (NIDDM). The levels were 0.924 ± 0.141 and 0.176 ± 0.036 g/l respectively, significantly higher than in healthy controls (n = 25) (0.674 ± 0.115 and 0.117 ± 0.013 g/l) (P < 0.001 and P < 0.001 respectively). In the NIDDM group, TSA and LSA concentrations in the angiopathic subjects (0.997 ± 0.068 and 0.183 ± 0.029 g/l) were also significantly higher than in the uncomplicated subjects (0.845 ± 0.062 and 0.163 ± 0.023 g/l) (P < 0.001 and P < 0.001 respectively). Angiopathic subjects were further grouped as being nephropathic or retinopathic and were also compared with the healthy controls and with each other. However, TSA and LSA concentrations did not correlate with the duration of diabetes nor with fasting plasma glucose, total cholesterol, triglyceride concentrations or glycated haemoglobin (HbA(1c)) levels. In conclusion, TSA and LSA may become distinctive parameters in NIDDM patients particularly in nephropathic and retinopathic subjects.