dtgreene: Your MP only regenerates up to a certain amount that depends on your character's class and INT (DEX on NES due to what I suspect is a translation mistake); if your MP is already full, you won't get any more.

Also, Fighters and Shepherds don't get any MP, and can't ever cast spells. (Well, in the NES version, they can eventually, but not on other versions.) If your main character is one of those classes, you will need to recruit somebody who can cast spells in order to have access to magic (and I'm pretty sure there's at least one item you can't realistically get without magic). Alternatively, you could just start over (and doing so might be a good idea if you're a Shepherd).

The MP amount for each class is as follows:
* Fighter, Shepherd: 0
* Tinker: INT / 2 (no access to more expensive spells)
* Bard/Paladin/Ranger: INT (possible to access every spell with this amount)
* Druid: INT * 1.5 (but note that Druids get poor INT growth at level up on PC)
* Mage: INT * 2 (can cast the most powerful spell right away)

By the way, one thing to note: The NES version is so different it might as well be a different game. The structure of the game is still about the same, and the maps are similar, but the game mechanics are completely different. (I do note that MP does work the same way on NES, except that walking around in towns doesn't refill your MP on NES, and that the DEX and INT stats are mislabeled on NES.)

Edit: Why did you post in a long dead topic rather than making a new topic? A new topic would be far more visible, and you could even have given it a better title than just the game's name (something like "[Ultima 4] MP not regernerating", for example).