Adsorption and two-dimensional (2D) condensation of 5-fluotocytosine on hanging mercury drop electrode is studied in this work. 5-fluorocytosine is an important derivative of cytosine which is widely used in pharmacology. The influence of concentration, temperature pH and electrolyte composition on the 2D condensation of 5-fluorocytosine was investigated by differential capacitance measurements. Three capacitance pits associated with the formation of 2D compact layers are evidenced. One film, formed at potential slightly negative from the potential of zero charge of the electrode, involves both neutral and protonated 5-fluorocytosine molecules. At highly negatively charged electrodes, dipole-induced orientation of 5-fluorocytosine leads to the formation of two additional 2D layers. One of them is found to result from the interaction of 5-fluorocytosine with acetic acid, present in the buffer electrolyte. Replacing acetic acid by other carboxylic acids does not affect the appearance of the film, suggesting that the carboxylic group is directly involved in the stabilisation of the 2D condensed layer. (C) 2011 Elsevier Ltd. All rights reserved.