OPA is often used as an off-line derivatisation agent for fluorimetric detection in gentamicin analysis. As, in general, electrochemical detection is more sensitive than fluorimetric detection, the analysis of gentamicin as its OPA derivatives by high-performance liquid chromatography and electrochemical detection is proposed. The derivatisation procedure is that described by the European pharmacopoeia. The method allows not only the detection of all major gentamicin congeners C-1, C-1A, C-2A and C-2 but also of other minor unidentified components. A full validation of the method is presented and comparison is made with fluorimetric detection. A good linearity is found for the four congeners within the dynamic ranges 1-50 mug ml(-1) for electrochemical detection and 4-80 mug ml(-1) for fluorimetric detection. Both methods presented good accuracy and fidelity, although electrochemical detection is more sensitive than fluorimetric detection. The electrochemical detection method presented in this work appears to be a good alternative to the fluorimetric and pulsed electrochemical detection methods. (C) 2004 Published by Elsevier SAS on behalf of Academie des sciences.