Interplay has branded claims by Bethesda that it only holds the rights to use the Fallout name - and no other assets - for its in-development MMO as "absurd".
Interplay sold the Fallout series to Bethesda in 2007, but then licensed back the rights to develop a Fallout MMO under certain conditions, which have been being disputed for some time now.
Bethesda sued Interplay last year over perceived misuses of the rights to the Fallout franchise, and the legal battle shows no signs of drawing to an amicable conclusion.
Bethesda's most recent legal filing claimed Interplay had licensed only "one single asset", the rights to the Fallout name, in connection with an MMO, and that any such game could not feature assets from the wider Fallout universe like characters, settings or storylines.
But Interplay disputed this assertion in a strongly worded legal response this month obtained by Gamasutra.
It reads: "Bethesda's interpretation requires Interplay to develop and release an MMOG under the Fallout name, but unrelated to the Fallout brand.
"First, this is not only absurd, but is specifically prohibited [emphasis Interplay's] by the agreement because Interplay was only granted a 'license and right to use the Licensed Marks on and in connection with its FALLOUT-branded MMOG ... and for no other purpose.
"It was not the parties' intent that Interplay create, for example, an online baseball game or poker game called 'Fallout.'"
Using the Fallout name alone and nothing more would deny Interplay "the fundamental benefit of using the trademark", Interplay argued.
This won't be the end of it, that's for sure.