$PATH

What's setting my $PATH to /bin:/usr/bin:/usr/bin:/usr/ucb?  It happens when I run xterm, but:
me@comp:~$ su me
Password:
Executing ~/.bashrc...
me@comp:~$ echo $PATH
/bin:/usr/bin
and su - gives me the correct $PATH:
me@comp:~$ su - me
Password:
Executing ~/.bash_profile...
Executing ~/.bashrc...
me@comp:~$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/games:/usr/local/pspdev/bin
How would I go about finding the file that changes my $PATH?
Is there any way of finding out what files XTerm executes on startup? xterm(1) doesn't tell me anything about that in the files section. Is it even XTerm?
Google isn't helping (or I am searching completely the wrong things).

/etc/profile and ~/.profile as well as /etc/bash/bashrc and ~/.bashrc, ~/.bash_profile, ~/.bash_login and possibly others.

man bash is a good start.

I managed to fix it by adding the line XTerm*loginShell: true to my ~/.Xresources file.