A method and device for transmitting a message from a first node device to a second node device, the devices using powerline communications. The first node device is able to send and receive fragments of the message on at least one frequency band using powerline communications and over a radio channel. The first node device, prior to the transmission of the fragment: estimates, for at least one frequency band, the theoretical duration of transmission of the fragment on the frequency band, and for the radio channel, the theoretical duration of transmission of the fragment on the radio channel, obtains, from a database, the result of integration of the degree of occupation of the frequency band and of the result of integration of the degree of occupation of the radio channel, selects, from the results of integration, the frequency band or the radio channel and transmits the fragment.