1. An exercise test has been developed which is suitable for elderly or frail subjects. It is based on free walking at three different speeds on a level indoor course of 256 m. The subject sets his own pace in accord with simple instructions. 2. Twenty-four elderly men and ten young men took part in the study. 3. The time and number of paces taken to cover two sections of 100 m within the course were used to establish that the subjects walked steadily. Walking speed, pace frequency and stride length were then calculated. 4. Heart rate was obtained with body-borne tape recorders and related to the walking speed. The heart rate at a standard walking speed could then be obtained by interpolation. This is an assessment of the cardiovascular response to exercise (physical condition). The variation on repeating the test was ±5% and there was no significant difference between the two age groups. 5. The assessment was found to correlate moderately well with a conventional assessment of physical condition based on oxygen uptake from tests on a bicycle ergometer. 6. The test could also be used as a performance index since walking speed was characteristic for the subject. The younger group walked significantly faster than the older group. As a performance index the test is therefore sensitive to age differences.