The purpose of this study is to introduce an area micrometerfor measuring the cross-sectional area of soft tissue. Havingmeasured the depth of PT of rabbit repeatedly, we found the coefficientof variation of this micrometer is less than 0.9%. Compared withnormal group, the cross-sectional area of PT in immobilized groupincreased significantly. This change may be relevant to the level ofcollagen metabolism of PT.