Parallel.ForEach() vs. foreach(IEnumerable<T>.AsParallel())

Erg, I'm trying to find these two methods in the BCL using Reflector, but can't locate them. What's the difference between these two snippets?

A:

IEnumerable<string> items = ...

Parallel.ForEach(items, item => {
   ...
});

B:

IEnumerable<string> items = ...

foreach (var item in items.AsParallel())
{
   ...
}

Are there different consequences of using one over the other? (Assume that whatever I'm doing in the bracketed bodies of both examples is thread safe.)