1) An electron microscopic study of the boundary tissue of the human seminiferous tubule was made on our 38 clinical cases, including 8 of normal adults, 11 of oligospermic and 19 of azoospermic patients.2) The boundary tissue of the human adult seminiferous tubule shows three layers: a basement membrane, a fibrillar zone of collagen fibres and a cellular zone of fibroblasts with a few collagen fibres.The last two layers constitute the so called tunica propria.3) The basement membrane is seen to be a mono-or tri-laminar structure of about 0.1μ in thickness, but it shows in some parts polylaminar approximately 0.5μ thick and some polylaminar projections into the seminiferous tubules are also present.4) In the boundary tissue only the presence of collagen fibres is confirmed, but the presence of those of elastic and reticulum fibres seen by the light microscope can not be proved.5) There are two types of fibroblasts in the cellular zone.Most of the fibroblasts are resting fibroblasts and another few are proliferating ones.6) In the boundary tissue of the human seminiferous tubule cells resembling smooth muscle, which were ascertained in rats by some authors, are not found.7) The pathologic changes of the boundary tissue in infertile men are listed below.i) basement membranea) obscure laminar structureb) irregular twistingc) increased numbers of the projectionsd) thickeninge) atrophyf) presence of foldings of the basement membrane towards the fibrilar zoneii) Tunica propriaa) fibrillar zone: thickening of the fibrilar zone by increased collagen fibresb) cellular zone: increased thin extensions of the fibroblast8) The above-mentioned pathologic changes are generally mild in the oligospermic cases. The changes of the basement membrane are seen only in a few oligospermic cases, but those of the tunica propria are recognized in about a half of the oligospermic cases.9) Generally in the azoospermic cases without any obstruction of the epididymis or vas deferens the most of the above-mentioned pathologic changes are pronounced.10) The so called thickening of the basement membrane seen by light microscope is found to be electronmicroscopically as a thickening of the fibrillar zone by increased collagen fibres.11) In mild cases of peritubular fibrosis a thickening of the fibrillar zone in combination with an increase of the thin extension of the fibroblast is also seen.12) In severe cases of peritubular fibrosis, a thickening of the fibrillar zone is marked, but the thin extension of the fibroblast is obscure.