Guinea pigs were acupunctured at "ZuSanli" (ST 36) with one direction twirling manipulation until an objective sensantion was felt by operator's hand. Frozen sections and scanning electromicroscopic specimens were made from the whole guinea leg acupunctured and were observed under light microscope and scanning electromicroscope respectively. In all specimens, a puncturing pore and different transformation of surrounding tissue were seen clearly. In hypodermis the connective tissue fibers circling the puncturing pore appeared as whirly form. In muscle layer, the connective tissue fibers of endomysium circled the pore and the relative muscle fiber were twisted and dislocated. Adjacent vessels and nerves were dislocated and transformed. It is infered that various needling sensative tissues and structures were simultaneously stimulated by twirling needle force, with connective tissue being as mediator, which is likely of the biological basis of needling sensation and ist complexity.