The plasma concentration of 1,5-anhydro-D-glucitol(AG)(1-deoxyglucose) is known to decrease in diabetic patients. In order to evaluate the usefulness of this polyol as a diabetic marker, we examined the specificity of the plasma AG reduction in various diseases: the plasma AG level was determined in 108 newly diagnosed diabetic patients, 229 normal subjects and 200 patients with various other disorders. The mean plasma AG concentration in diabetes mellitus was 1.9 +/- 1.8 micrograms/ml (mean +/- SD), which was definitely lower than that in healthy subjects and patients with other diseases including some metabolic and hormonal diseases (mean value range: 13.4-28.3 micrograms/ml). Only the "malignancies" group showed statistically different mean values from that in normal subjects; however, these values were much higher than those of diabetic patients. The AG concentration seemed to be relatively low in some severe by uraemic patients, but is likely to be little influenced by the glomerular filtration rate. Upon adjustment for sex and age, AG concentration was not found to be correlated with the degree of obesity in both healthy subjects and diabetic patients. The plasma AG concentration showed a tendency to be higher in healthy males than in healthy females in all age-matched groups; however, statistically significant differences were not seen. Also, no significant influence of age was observed.