A system intended for being at least partly implanted into a living body and comprising at least two modules or devices which are interconnected by a communication transmission channel, at least one of said modules being provided with transmitting and receiving means for a bidirectional exchange of information with at least one further module and at least one other module of which being provided at least with receiving means or transmitting means for receiving information from at least one further module or for transmitting information to at least one further module, respectively. Within the intracorporeal region, said communication transmission channel by data modulated ultrasound. The body mass provides for an ultrasonic coupling between two or more implantable modules and/or between at least one implantable module and an external skin transducer intended for connection to an external module. The exchange of information is effected by modulated medium frequency signals in the frequency range from 10 to 100 kHz, which signals are passed through said communication transmission channel and transmitted or received by ultrasonic transducers, e.g. piezoelectric crystals.