Current methods of recording the fallopian tube motility in vivo essentially measure the intraluminal pressure. Diametral change is another parameter which can provide additional useful information related to tubal function. A method for in vivo monitoring of diametral change without obstructing the lumen and based on the impedance measurement technique has been proposed. An in vitro comparison of wall displacement with transtubal electrical impedance change shows that the impedance changes reflect diametral changes. Another in vitro experiment in which the autorhythmicity of contractions was maintained by means of a perfusion bath indicates that the impedance changes are primarily due to the contraction of the circular muscles of the fallopian tube. These studies were followed up with long-term chronic implantations with dual probes on the isthmic and ampullar regions of the tube in female rabbits. Inpedance changes over periods as long as 6 mo could be readily obtained. Histological observations as well as fertility studies support the conclusion that the tube is minimally affected by the placement of the probes.