The response of skin blood cell flux (SBF) to locally applied pressure was evaluated with the laser-Doppler technique in the areas of the sacrum and the gluteus maximus muscle of geriatric patients and healthy young and elderly subjects. The SBF over the sacrum stopped at a lower external skin pressure than over the gluteus muscle in all groups studied (P less than 0.05-0.001). The SBF at rest was lower among geriatric patients and over the sacrum, with men showing the lowest value (P less than 0.001). The initial slope of the SBF curve and the peak SBF during the post-occlusive reactive hyperaemia (PRH) were lower among geriatric patients compared to younger healthy subjects (P less than 0.05-0.01) over both areas studied. During the last part of the PRH response rhythmic oscillations started, known as vasomotion. The mean skin temperature at rest was higher over the sacrum (P less than 0.001) than over the gluteus area, but no difference was found between the groups. The temperature increase during the PRH was larger over the gluteus muscle (P less than 0.01) than over the sacrum area in the healthy subjects. Among the patients the temperature increase was larger over the gluteus only during the first half of the PRH, after which the temperature increased most over the sacrum. It is concluded that SBF and skin temperature show different responses in microvascular reactivity to external pressure in elderly vs. younger subjects and also between sexes. The described technique may be useful in clinical practice for predicting the risk of pressure sores in different areas and subjects.