A recent deal between the Smithsonian Institution and the Showtime Networks cable channels has some documentary filmmakers, historians and researchers concerned that their access to the collections and curators of the Smithsonian could be limited or cut off.

This month, Showtime and the Smithsonian announced the formation of Smithsonian Networks, a joint venture to create television programming, including documentaries and short films, that draws on the Smithsonian collections and staff to explore scientific, cultural and historical events. The first venture of Smithsonian Networks will be an on-demand cable channel, scheduled to begin in December.

Under the agreement, the Showtime-Smithsonian joint venture has the right of first refusal to commercial documentaries that rely heavily on Smithsonian collections or staff, said Linda St. Thomas, a spokeswoman for the Smithsonian. That means that a filmmaker who does not agree to grant Smithsonian Networks the rights to the film could be denied access to the Smithsonian's public collections and experts, Ms. St. Thomas said.