When an National League team plays an American League team during the regular season, what rules do they use? The home teams?

The home team, if the game is in an AL park, then they have the DH, if it's in an NL park, the pitchers get to bat.

The rules apply to whichever team is the home team, if they play in an AL park, they use DH, if they play in a NL park, then the pitcher bats

Yes, the home teams league rules apply.

dh is used at a.l. home team parks and pitchers hit on n.l. fields

Interlaegue play is over for the season.

Both leagues are goverened by MLB rules...so same thing applies in both leagues.

Only difference is in NL parks the pitcher bats.
In AL parks they use the DH.

The home team's league rules apply.

Yes they use the home teams rules. American league park American league rules, National league park Natonal league rules

As mentioned in everyone else's answers - it's the home teams rules that apply.

Yeah....the game is played like the home team would usually play it.So if it is an NL stadium then the pitcher bats but if it is in an AL stadium then there is a DH.

Yep. They go by the rules of whatever ballpark they're playing in. It doesn't matter if its interleague play, the All-Star Game or the World Series.

American League park = American League rules and vice versa

I recently read an interesting article by Tigers pitcher Todd Jones advocating a switch of that. He thinks it would be interesting to let American League crowds see a game played by National League rules and let National League crowds see a game with DHs. If you're going to hold interleague play, why not? It sounds like fun.

If the games are played in the american league parks the american league rules apply, for example the DH is used only in a.l. parks. and while in a NL park their rules apply. It is the same as the world series.

The rules of the league that the home team is in apply. So the DH is used in American League parks and pitchers bat in National League parks.