why does the directory /tmp show 100% usage on Red Hat Enterprise Linux 4

Issue

Directory /tmp is full on our server running on Red Hat Enterprise Linux AS release 4 (Nahant Update 8) machine. Why does the directory /tmp is showing up as full?

[root@server1 tmp]# df 

/dev/mapper/VolGroup_ID_2-LogVol2 
                        507748    481906         0 100% /tmp 

When we do an ls -la on the directory, we cannot seem to find what's consuming the space.  Is there a command we can use to recursively search the directories in /tmp to try to figure out what's consuming all the space?  Our manual investigations of cd into the directories and doing ls -la's have turned up nothing.