IPython & subplot

I'm just playing with matplotlib inside IPython for my first time and want
to do the equivalent of:

In [1]: subplot(211)
In [2]: plot([1,2,3])
In [3]: show()
-> displays as expected, in the upper half
Now I want to interactively display a 2nd plot in the bottom, but when I do:
In [4]: subplot(212)

I get a new, single empty plot displayed in the lower half.
Is there some 'hold' cmd I'm missing to do this?