[DrDouble]

I know it is standard to lead the highest doubleton in defence, but does this apply to Kx where x is not an honor.

[awm]

Yes. If you are going to lead from Kx it is normal to lead the king. This potentially unblocks the suit -- for example if partner has AQxx you can cash the first three tricks this way, whereas leading low you could not do so.

However, usually leading from Kx is not really the best suit to lead (unless partner bid the suit of course) and it might be advisable to look for a different suit to attack.

[mtvesuvius]

Yes, this is the standard treatment, and even people who lead low from doubletons would lead the K from Kx for the reasons Adam stated... Kx leads are trivial. Against Notrump however I find that often they work in auctions where both opponents have denied a 4 card major, because you will almost always hit partner's 5 card suit, and if you have very little points with no entries it's usually better to establish partner's suit than your own becuase you will have no entry to get in and run the suit, even if you have some points it's still often best to set up partner's suit. Against suits you are obviously looking for a ruff, so you will usually want a trump entry before lead the King from Kx. There are other times when it is right, but these are the main situations.

[Codo]

Anybody leads the Honour from Honour x when he must lead the suit.
But not anybody leads high from a doubleton. There are millions out there who lead low, depnending on their leading agreements.

[kenrexford]

You lead small from Kx against a slam when dummy bid the suit and you want to force a round-one guess for all the marbles.

Otherwise, duh!