Is there a salt antidote?
Depending on the exact dish, a possible solution I have found (and tried) is to add potatoes to the dish, leave for a while (30 mins or so) then remove.  They are meant to absorb the salt somewhat.  It didnt work for me however.

What is the dish you are having problems with?  If it is something with a sauce (e.g. Stew) I have before had to strain it to remove some sauce and then add more stock/water to dilute it back down to your desired consistency.