We studied the tensile strength and collagen content of the amniotic membrane in the early and late second trimester and at term in specimens obtained after spontaneous, cesarean, and prostaglandin- and stretch-induced deliveries. No significant difference in either tensile strength or collagen content was found among any group of samples. Collagenous tissue of the amnion seems to differ constitutionally from that of the cervix and vagina and to be modulated by different mechanisms during pregnancy and delivery. It also seems to resist strong physiologic tension until it is mechanically ruptured during delivery