Abstract: Apparatus with facing bell members for modified-atmosphere packaging of products contained in trays, comprising at least three circuits: a first circuit and a second circuit (24, 25) which are connected to the main chamber (P) enclosing the internal volume of the trays and open out in different positions (23, 23?) of this volume and a third circuit (17) connected to the internal chambers (2, 9) of the bell members (1, 8) and these circuits are intercepted by respective valve means (28, 128, 18, 118) so as to be initially all connected to the vacuum means (21, 121) and then the said first circuit (24) is closed, while the said second circuit (25) is connected to the means (26) for introducing the service gases which, entering into the tray, force the remaining air out so as to occupy a small buffer formed by the said second closed circuit (24, 28).