A system for displaying the positions of substances in electrophoretic separations comprises a gel (635) a substance to be separated into a region (450), plates (400, 401) with electrodes (405-420 and 430-445) placed on either side of the gel. A source (315) applies a voltage to an electrode on one side of the gel, and an electrode on the other side of the gel is connected to the input of an amplifier (320). Multiplexers (605, 610) connect the source and amplifier to electrodes on either side of the gel. A computer (600) issues commands to the multiplexers to connect the source and amplifier to individual electrodes, and while a pair of electrodes is so connected, the computer activates a sample-and-hold circuit (620) and an A/D converter (630) to record the value of the electrical impedance within the gel at the location of the selected electrodes. The impedance value is stored in the computer's memory and also displayed on a monitor (635) connected to the computer. The result is visualization of a gel-electrophoretic separation without requiring the use of stains, radioactivity, or molecular tags.