The application of isothermal calorimetry for the early detection of the resistance of wild oat to fenoxaprop(1) and diclofop(2) was investigated. In the first test, three leaf tillers were sprayed with field doses of fenoxaprop or diclofop. For resistant biotypes, the rate of heat flow after 48 h was similar to that in control plants. In susceptible biotypes, fenoxaprop significantly reduced and diclofop significantly increased the rate of heat flow. In the second test, 3-day-old seedlings were put into calorimetric ampoules on filter paper moistured with herbicide solution (152% and 40% of the field dose for fenoxaprop and diclofop, respectively). Rate of heat flow was measured for 72 h, however, differences were already visible in the first hours of germination on each herbicide. Rate of heat flow for seedlings resistant to both herbicides was higher than for susceptible ones. The most evident differences between susceptible and resistant biotypes were noticed after 10-20 h and 25-40 h (of the seedlings' growth) on fenoxaprop and diclofop, respectively, when a sharp increase of rate of heat flow was observed. In conclusion, calorimetry may be used as a rapid test for the detection of the resistance of wild oat biotypes to fenoxaprop and diclofop. (C) 2005 Elsevier B.V. All rights reserved.