Partner opens 1NT.
With a 4 carder Spade and a 5 carder Heart, what do you do?
And with a 5 carder Spade and a 4 carder Heart?
Specifically, should you use Stayman, Jacoby Transfers, or some other convention?
The most common answer to this problem is called Smolen, which applies when you have game-forcing values. In Smolen, you start with Stayman. If partner shows a 4-card major, proceed as normal with that suit as trumps. If partner denies a major, you bid your 4-card major at the three level. Opener now chooses a strain.
With less than game-forcing values, your choices really depend on what other bids mean in your system, but the following is usually workable:
As ruds points out in his answer, the expert treatment here holding game-forcing or better values is to play Smolen Transfers. In this case the auction has gone:
1NT pass 2C pass 2D pass ?
and (with * indicating the alertable transfer calls):
- 2H shows game-invitational (only) values with exactly 4 spades and 5+ hearts;
- 2S shows game-invitational (only) values with exactly 4 hearts and 5+ spades;
- 2NT 9 points, invitational in NT;
- 3C game forcing, 5+ (usually 6) clubs, no 4-card major;
- 3D game-forcing, 5+ (usually 6) diamonds, no 4-card major;
- 3H * game-forcing, with exactly 4 hearts and 5+ spades;
- 3S * game-forcing, with exactly 4 spades and 5+ hearts;
- 3NT to play
With less than game-invitational values you have fewer choices, and tougher decisions:
Holding 22 distribution in the minors and a weak 5-card major it is probably best to pass and just play 1NT. If the opponents come in they may get a nasty shock from the unfavourable distribution waiting them in the majors.
With 31 or 40 distribution (either way) in the minors or a strong 5-card major you should simply transfer into your 5-card major and pass partner's rebid.
With a bust three-suited hand, short in clubs, it is possible to play Garbage Stayman and simply pass partner's response to 2C. Unless playing Matchpoints I would not recommend this without 5 diamonds and 4-3 or 3-4 in the majors.
It is possible to play Crawling Stayman over partner's 2D response, but this will cost you precision in game-invitational auctions; it is strictly a Matchpoints convention, where part-score auctions are of increased importance.