We studied the effects of dietary fiber polydextrose feeding on plasma lipids and changes in diurnal plasma sugar, insulin and blood pressure levels. Seventeen patients were entered into the study. Polydextrose (15g/day) was given to the subjects for 4 weeks. Plasma total cholesterol (TC) and lowdextrose (15g/day) was given to the subjects for 4 weeks. Plasma total cholesterol (TC) and lowdensity lipoprotein cholesterol (LDL-C) levels were reduced by 6% by polydextrose, but these changes were not significant. Plasma apo (protein) B concentrations were significantly decreased (p<0.05). Polydextrose did not affect the diurnal changes in plasma sugar levels, but significantly decreased the level of plasma insulin at 2h after dinner (p<0.02) and at midnight (p<0.05), respectively. In mildly hypertensive patients, the systolic blood pressure between 12: 00 and 18: 00h and the diastolic blood pressure between 18: 00 and 24: 00h were significantly decreased, respectively (p<0.05, p<0.05). Urinary Na/K excretion ratio was slightly increased by polydextrose. The effects of polydextrose on blood pressure seemed to be related to the decrease in plasma insulin levels.