Terms of the transaction were not disclosed, but since the Bengals tagged Spikes as a transition player, they have seven days to match the offer and retain their defensive captain. If their elect not to match, they will not receive compensation.
Spikes, the team's leading tackler four times in his five seasons with the Bengals, has made it clear he has had enough of the losing in Cincinnati. In his five years there, the Bengals are 19-61.
New Coach Marvin Lewis, a longtime defensive coordinator in the NFL, placed the transition tag on Spikes because he wants to retain the key building block for the defense.
The Bills want Spikes for their defense, and have cleared more than $5 million in salary cap space by trading wide receiver Peerless Price to the Atlanta Falcons for a first-round pick in the 2003 draft.
"We could have put together an offer sheet even if we didn't make the trade, but yes there is more room (under the cap)," said Buffalo General Manager Tom Donahoe.
Last week, Donahoe signed free agent Jeff Posey to start at strongside linebacker, and hopes to have Spikes on the weakside to surround middle linebacker London Fletcher.
Buffalo ranked 27th in points allowed last season, 29th against the run, and last in the league in takeaways.
The Enquirer reported Buffalo was Spikes' only visit, and Donahoe talked to former Bengals coach Dick LeBeau about him.
"He brings a lot to a team in terms of intensity and leadership," Donahoe said.