With acidic aqueous mobile phases on silica, detection by electrochemical oxidation on a carbon paste working electrode was compared with detection by the native fluorescence by excitation at 280 nm of catechols and indoles. Based on evaluations of sensitivity, reproducibility, stability, selectively and simplicity of handling, the fluorescence detector was considered superior to the voltammetric detector. Preliminary results from direct injections of deproteinized serum indicated that at levels of at least 10 microgram/1 the content of some indoles in biological fluids could be determined without further sample purification.