can't load lib in /usr/local/lib

[hcchin]

    After I instll xmllib in /usr/local/lib, the program still can't find 
libxml.so.1, even if I include /usr/local/lib in PATH, is still don't 
work, but if I set a link in /usr/lib,

    ln -s /usr/local/lib/libxml.so.1 libxml.so.1

    It will work, I assume that there is a setting, but where is it?