A sophisticated variation of Blackwood in which the king of the trump suit is like a ‘fifth’ ace; the four aces and the king of trumps are all key cards. The usual responses to 4NT are:
5♣ 0 or 3 Key Cards 5♦ 1 or 4 Key Cards*.
5♥ 2 or 5 Key Cards but not the queen of trumps*.
5♠ 2 or 5 Key Cards including the queen of trumps.
After a 5♣ or 5♦ response, the 4NT bidder may continue with a bid in the lowest non-trump suit to enquire about the queen of trumps. The responder returns to the trump suit at the lowest level without the queen or, with it, bids 5NT or cue bids a second- round control. An alternative method is for responder to proceed: one step without the queen, two steps with it.
* Some partnerships interchange the meaning of the 5♣ and 5♦ replies, the thinking being that the 4NT bidder is more likley to want to enquire further facing 1 than 0.
The 4NT bidder can continue with a bid of 5NT to ask for the non-trump kings. Responses can be to show the lowest king or on the standard step principle:
6♣ 0 King
6♦ 1 King
6♥ 2 Kings
6♠ 3 Kings
Roman Keycard Blackwood is a powerful tool and popular amongst tournament players.