Isothermal tanks are widely used for transport of perishable liquid foodstuffs like milk, wine, juice etc., and according to the international ATP Agreement, they have to be tested periodically in officially recognized national ATP Test Stations to ensure that they meet the specifications. The testing of a multicompartment isothermal tank presents special difficulties in comparison to the testing of a refrigerated truck because of the number of compartments that have to be measured. The instrumentation needed for testing a specimen in these cases is complex and that is why only a few ATP Test Stations can conduct such tests. In this study, a heat transfer numerical simulation is described of a multi-compartment isothermal tank for the transport of perishable liquid foodstuffs tested at a new environmental ATP chamber recently constructed at the Zografou Campus of the National Technical University in Athens. The tests were conducted according to the regulations specified in the United Nations ATP Agreement. A transient finite difference model is developed for a typical specimen multi-compartment isothermal tank tested inside an ATP Testing Chamber. To adjust the cooling or heating system, a PI controller is used. The simulation results are compared to experimental measurements under real conditions and show good agreement. The study describes also a method for testing multi-compartment isothermal tanks according to the ATP specifications using only the measuring equipment normally existing in every ATP laboratory. With the proposed method, the testing of a three compartment liquid foodstuff tank is possible using only one heating capacity adjuster, e.g. one PI controller and one thyristor instead of the three independent PI controllers and three thyristors normally needed in order to adjust the required heating capacity inside each compartment. (C) 2004 Elsevier Ltd. All rights reserved.