The adsorption of hypoxanthine on a mercury electrode from sulfate solutions 0.2 and 0.5 at pH 2.0 and 5.0 is studied. Differential capacity, zero charge potential and maximum surface tension measurements are used to establish the characteristics of the dilute layer. Condensed film formation is reported for first time, detected from differential capacity data at high hypoxanthine concentrations in solutions at pH 5.0. The data for the dilute layer conform to a Frumkin isotherm, contrary to previous findings about a Langmuir isotherm. The data are also analysed following the Nikitas approach and a value for the size ratio parameter close to one is obtained. The discussion in terms of Esin-Markov effect and electrosorption valency in comparison with other aromatic compounds allows some conclusions to be drawn about the orientation of the molecule, the role played by electrostatic and pi-electron interactions and the effect of intermolecular interactions.