It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

×
I'm not sure if it works or not with the GOG version, but a review linked to here: http://www.3drealms.com/duke1/index.html -> scroll down to Downloads -> duke1ed.zip

Let others know if it works (I can't test it), if there are special things needed to get it working, etc.