newbie: problem with page.replace

I'm going to add some functionality to my application. I need to
replace two page's elements with each other.
All works fine, but I would like to refresh only changed elements, not
all on the page.
I think ajax should hel me but I have a problem with rendering the
replaced elements.

In the .rjs file I have:

page.replace, '<h1>test</h1>'

and this works - it pretty replace appropriate element with given html
string and also render the page correctly.

But this one, doesnt work at all.
page.replace, :partial => "replace2"

In the _replace2.rhtml I have a temporary text like:

Does someone know what could be the reason of this? Why :partial makes
that nothing is rendered?

Thanks in advance for any answers.