Transactions within plpgsql functions?

Is there any way to have transactions work inside plpgsql procedures? So far
none of my attempts have worked. It's kind of frustrating to have to wait
days for results and especially so when the procedure terminates
unsuccessfully saying that I've done too many operations (more than 2**32
database operations in my setup).

Yes - I know that I could have procedures calling procedures to get what I
want, but this seems a little awkward.

Thanks for any assistance.
Celia McInnis