Content-based networking fosters a new kind of communication in which information flows towards interested hosts rather than towards specifically set destinations. Supporting this kind of communication in mobile ad hoc networks is still a challenge, though, especially in partially or intermittently connected networks. This paper addresses this problem by combining the concept of content-based communication with that of opportunistic networking. The protocol it describes exploits transient contacts between mobile hosts that exchange messages according to their respective interest profiles. A message thus disseminates in the network by being stored, carried, and forwarded by those hosts that show some interest for this message. Experimental results as well as simulations confirm that this approach makes it possible to disseminate information efficiently, while minimising the resources implied in this dissemination.