High pressures on the soles of the feet of diabetic patients cause plantar ulcerations, and reduction of this pressure is important in the treatment and prevention of such ulcers. The effects of foot orthoses on the distribution of plantar pressures were investigated using a pressure-sensitive insole containing 960 sensor elements in seven diabetic patients (13 feet) with diabetic ulcers or past histories of diabetic ulcers. Plantar pressures at the foot-insole interface and their distribution were measured in a stable standing position wearing the patients' own shoes, with and without foot orthoses. The preorthotic peak pressure was 130.6 +/- 41.9 kPA (mean +/- S.D.), while the postorthotic peak pressure was reduced to 52.6 +/- 17.9 kPa (P < 0.001 vs. preorthotic). The mean reduction of pressure was 56.3%. The preorthotic contact area was 330.2 +/- 48.4 pressure-sensitive elements and the postorthotic contact area was increased to 517.2 +/- 105.5 elements (P < 0.001), with a mean increase of 62.7%. The marked reduction in plantar pressures at the foot-insole interface by pressure redistribution indicates that this new pressure measurement system is very useful for the design of such orthoses.