It is often difficult to estimate slight alterations in the severity of ataxia by bed-side neurological examinations. We analyzed the heel-knee tapping test, which has often been used as a standard bed-side examination to check incoordination in lower limbs, using a new motion measurement system "video/computer motion measurement system". We studied 9 normal controls and 21 patients with spinocerebellar degenerations (SCD). In patients with SCD, the up-and-down motion range of the heel was variable and the heel moved in the anterior-and-posterior direction, because of knee sways during the test. Following oral administration of TRH analogue, TA-0910, above-mentioned findings were clearly improved. Analysis of spatial and time elements of the knee joint demonstrated quantitative improvement. Therefore, an effect of TA-0910 on incoordination of the lower limbs could be proved objectively by a computer motion measurement system.