[en] The ever growing concern of modern societies about environmental pollution imposes serious responsibility on the analytical chemist who is entrusted with the task of monitoring the levels of both radioactive and conventional pollutants in various environmental samples. The main requirement for this service to be effective is that it must furnish reliable i.e. accurate and sufficiently precise results. Hence, the necessity of periodic checking of the analytical performance of any laboratory is now more and more widely recognized. Such a check-up is of importance both to laboratories newly entering the field which are but acquiring the necessary experience, as well as to renowned laboratories in which interchange of the staff, modifications of the procedure or simply excessive routine may also sometimes lead to erroneous results. The analytical quality control service of the IAEA has organized already in the past intercomparisons on the determination of certain radionuclides in simulated liquid milk. The success of these exercises has induced the Agency to organize the new intercomparison of this series in 1975-76, the results of which are presented in this report