Problems compiling nmap 3.98BETA1 on 5.10

[Dan]

Whilst running ./configure I get:

checking If you have GTK+ installed... Package gtk+-2.0 was not found in
the pkg-config search path.
Perhaps you should add the directory containing `gtk+-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtk+-2.0' found


I've seen this a lot... what packages do I need to install to have a
system where others apps can compile against the GTK+ environment?

Dan