Whole cells of Rhodococcus erythropolis were employed as a receptor of a microbial sensor for 2,4-DNP determination using an oxygen Clark-type electrode as a transducer. A linear relationship of the sensor response (the respiratory rate of R. erythropolis as receptor) to 2,4-DNP concentrations was obtained for concentrations in the range from 2 x 10(-5) to 20 x 10(-5) M. Dinitrophenol concentrations of above 10(-3) M inhibited R. erythropolis respiration. The sensor response to 2,4-DNP was shown to add up from two components: (1) the effect of 2,4-DNP as the respiratory substrate on the cells' respiration of receptor element; and (2) the stimulative effect of 2,4-DNP as protonophore on the cells' respiration. Dinitrophenol detection at concentrations of below 2 x 10 M can be realized using the influence of 2.4-DNP upon the cells respiration in the presence of ethanol as an additional exogenous substrate (co-oxidation effect'). The mechanism of the 'co-oxidation effect' is discussed. A relationship between the activity of R. erythropolis respiration on ethanol and the activity of respiration on 2.4-DNP was found to exist. The level of this activity is supposed to depend on the content of nicotinamide nucleotides in the cells and oxidation-reduction state of these nucleotides. (C) 2002 Elsevier Science Ltd. All rights reserved.