Highlighting inside a text in Beamer

[Manolo Martínez]

Hello,

I'm writing my first presentation with Beamer, and I've stumbled upon 
the following problem I'd like to have a quote such that the slide first 
presents the quote as it is and, then, when I push a key, one passage is 
highlighted first and, when I push again, another passage is 
highlighted. I cannot see any way to do this using \alert. Is there an 
easy way?

Thanks.
Manolo