Snapping the four-day upward march, the Sensex fell over 34 points in opening trade today on profit booking at higher levels amid weak global cues. The 30-share index, which had gained over 441 points in the last four sessions, lost 34 points to 17,936 in opening trade today. The wide-based National Stock Exchange index Nifty also declined by 16 points to 5,359. Brokers said overnight weakness in the US markets and subdued opening of the Asian bourses triggered selling by foreign funds.