The Kinaesthetic Sensitivity Test (KST) was used to measure the development of kinaesthetic acuity in adolescent boys. Thirty boys were tested longitudinally, at intervals of 6 months, between the ages of 111/2 and 14 years. A second group of 20 boys was tested at the ages of 14 and 161/2 years. The findings were compared with existing normative data on 5- to 12-year-old children and young adults, and they indicated improvement in kinaesthetic acuity with age. Although the age effect is statistically significant only in the older group, confidence intervals show that the rate of improvement in both groups is comparable to improvement between the ages of 5 and 12 years. The reliability of the test is rather poor. The conclusion is that kinaesthetic development continues throughout adolescence. Further, development is quite robust and detectable even with a fairly unreliable measurement instrument. However, individual assessments should be interpreted with caution.