ltdl.h problems in ./configure

[Andrew Sackville-West]

Greetings --

I'm trying to complie 1.8.11 after using 1.8.9 from debian.

./configure returns

"configure: error: Cannot find ltdl.h -- libtool-devel not installed?"

google says I need to install libltdl3 which I've already got (actually 
apt-get reomved and installed just to make sure)

there is no package i can find called libtool-devel. I've seen reference 
to libltdl3-devel but can't find that and I think it might not exist.

any clues?

locate ltdl.h returns

/usr/share/libtool/libldtl/ltdl.h

is this in the wrong spot? how can I make configure find it?

thanks in advance.

Andrew