The 30-share BSE index, which gained nearly 357 points in the previous two sessions, fell by 92.97 points, or 0.56 per cent, to 16,405.50 in the first few minutes of trade today.
In a similar fashion, the wide-based National Stock Exchange Nifty index shed 28.55, or 0.55 per cent, to 4,920.35.
IT, metal, auto, oil and gas and banking stocks witnessed the most selling pressure, dragging down the Sensex.
Market experts said the early morning losses were caused by profit-booking as funds and retail investors cashed in on the handsome gains registered in the previous two sessions amid a subdued trend on other Asian bourses after credit ratings agency Moody`s downgrade of Japanese sovereign debt.
A strong rally overnight in the US market was also ignored by the participants, they said.
Furthermore, squaring up of pending positions by speculators ahead of monthly expiry in the derivatives segment on the National Stock Exchange tomorrow also cast a shadow over the trading sentiment, they said.
Meanwhile, in the Asian region, Hong Kong`s Hang Seng Index was down 0.45 per cent, while Japan`s Nikkei lost 0.19 per cent in morning trade today. The Dow Jones Industrial Average in the US rallied by nearly 3 per cent in yesterday`s trade.