importprivkey is an RPC command on bitcoind that allows a private key to be added to a wallet.

This is a Bitcoin 0.6.0 feature and is available in the 0.6 release candidates and later.

 $ bitcoind help [...]   importprivkey <bitcoinprivkey> [label] 

See Also on BitcoinWiki

• Sweepprivkey proposal

Source

http://bitcoin.it/