The Sensex resumed up at 25,528.80 and moved up further to a high of 25,606.92 on initial heavy buying on the back of good foreign capital inflows.
However, it dropped immediately to 25,358.71 at 1100 hrs, showing a loss of 130.86 points or 0.51 per cent.
The NSE 50-share Nifty also dropped 37.15 points or 0.48 per cent to 7,777.75 at 1100 hrs.
However, Dr Reddy's rose 3.33 per cent followed by Asian Paints 1.11 per cent, Lupin 0.67 per cent and Infosys 0.65 per cent.
Overseas, Asian stocks logged gains, shrugging off soft Chinese data released over the weekend. China's investment, factory output and retail sales all grew more slowly than expected in April, adding to doubts about whether the world's second-largest economy is stabilizing.
Meanwhile, the India Meteorological Department (IMD) yesterday said the monsoon onset over Kerala this year is likely to be slightly delayed.
