Indirect thermo-optical detection for capillary electrophoresis is described first. A 20 mW helium-neon laser (632.8 nm) was used to provide the pumping beam and a 2 mW helium-neon laser (632.8 nm) supplied as the probe beam; Methylene Blue dye was used as a background absorber. The addition of ethanol to the background electrolyte solution can be performed to reduce adsorption of Methylene Blue onto the capillary wall. The detection method was applied to the detection of amino acids separated by capillary electrophoresis. The detection limit for lysine was 5 x 10(-6) mol l(-1) (signal-to-noise ratio, 2).