The proliferation of new distributed application raises new requirements in term of communication functionalities such as group communication and quality of service handling. After a description of multicast services in ATM networks, we present an extension of the ATM multicast service to support multicast sessions with both dynamic and heterogeneous quality of service. Our proposed approach is based on integrating at the ATM switches QoS handling processes along with the required signalling procedures required to handle members join and leave in such environment.