Adsorption of terbutylazine and atrazine on a mercury electrode was investigated by means of time resolved capacitance measurements and phase-sensitive a.c. polarography. Both compounds form compact adsorbed layers. The temperature dependence of the capacitance yields a critical transition temperature of the compact film formation, which is higher for atrazine. Differences in condensation kinetics of both pesticides are correlated with their environmental contamination behavior. (C) 2003 Elsevier Science B.V. All rights reserved.