A device has been conceived to study the circumnutation of the bean tendrils (Phaseolus vulgaris). A detailed description of the device and preliminary results are presented in this article. The device permits the continuous recording of the tendril circumnutation and also the continuous control of the relative position of an external lateral factor, e.g. light, gravity. This is of particular interest if one wishes to study the influence of external factors on the circumnutation phenomenon. After data processing in a microcomputer program, the angular speed of the tendril and its relative position to the external lateral factor can be calculated for every sector of 30° rotation. A vectorial graph allows an easy and rapid evaluation of the circumnutation speed in relation or not with an external factor.