method and apparatus are disclosed for obtaining flow information of a conductive fluid by detecting the streaming potential and analyzing the resultant signal . in a particular embodiment for detecting abnormal blood velocities in the arterial tree , the apparatus includes a flexible sensor having two fixedly spaced apart electrodes and a common mode signal electrode . each sensor electrode is connected to an input of a differential amplifier and the common electrode is connected to the common input of the differential amplifier . the output signal from the differential amplifier , after filtering and amplification is provided to a recorder or oscilloscope so that it can be compared with the normal or average signal . a particular embodiment of the method is used to detect blood flow abnormalities , either too fast or too slow compared with most healthy individuals of the same age . in this method , a flexible sensor having two fixedly mounted electrodes is placed on the skin over the artery to be examined , for example the dorsalis pedis artery , so that each electrode is in electrical contact with a different part of the artery . the detected signal is processed and is compared to normal signals . these comparisons can be the wave shape or the time difference between the detection of the wave pulse and a pump timing signal such as the ecg signal .