Unfortunately, yes there is.
justjaredjr.buzznet.com/2009/03/03/high-school-musical...go/
It's been confirmed, and Matt Prokop (Jimmie) has said on his myspace that he is not going to be in it.

I think this is gonna ruin the series. And what was the point in introducing new characters if you're not gonna use them? Ugh, Disney sucks.

i dont think that there is goin to be another high skool musical.Bcuz pl will b talkin bout it and i aint heard nuttin so there it is idk!!! soy mexicana 100%

It's not silly...b/c i don't even know. Mystery??

Yes but unless you dont like zanessa you should watch it.

Zac Efron and Vanessa Hudgens arent going to be in it. Kenny asked they said no so...there geting dum replacements

Yes there is,but the orignal cast isn't going to be in it .ugh this wholer HSM should have stopped at HSM3 its so annoying at times ,like Zac Efron is so girly looking

no i dont think so.

there is defently going to be a hsm 4 just that gabby troy ryan sharpay taylor or chad is not going to be in it

Yea there is but it is going to have different actors. :(

Yes, there is going to be one but some of he crew are not going to be there. Like Jamie (my favorite) and some others...

yes there is but zac efron +vanessa hugens+corbin bleu+ashley tisdale and the others wont be in it.

Oh Yes there is. If there wasn't i was gonna march to that door and tell them that they r dissapointing fans of HSM. Jimmie,Rocetman, is my second hottie. Zac is my first hottie.

Some fans want a HSM4 and some don't.
I think that Disney may be considering to make HSM4, but personally, with or without one, I'm not fussed.
HSM3 was a really great and fun ending to the trilogy. But if they want to make HSM4, go ahead.
But since they have finished high school, they should stick with the name: High School Musical.