The problem is very unclear,

I have an application server, that constructs queries and sends it to Oracle to get response.

The Oracle database is installed on a high perfomance server:
Linux 2.6.18-194.el5 #1 SMP Tue Mar 16 21:52:39 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux

The application server was tested on different locations inside of the intranet, including that high perfomance server, where the database is located.

Several versions of the application server (from old to newest) were tested also.

The problem:

When the application server sends a query to the oracle apps dba, it has to wait for about 300 seconds to get response and construct logged output.

But when I'm connecting to the database with PL/SQL Developer and running that query using that IDE, I'm getting a response in less than one second.

Is there something familiar for you, guys?

We're just cracked our heads trying to determine where the problem could be located.

If you need more information - I'll update this post immediately.