Turkey's benchmark fell 189.72 points at the start of Friday trading to open at 89,680.96 points.
The BIST 100 index dropped 0.21 percent with the banking and holding sector indices down 0.07 percent and 0.04 percent respectively.
Among all sectors, the paper printing sector index was the best performer -- up 0.18 percent -- while the chemical, petrol and plastic sector index saw the greatest drop, falling 1.32 percent.
On Thursday's close, the BIST 100 was down 1,081.48 points or 1.19 percent to 89,870.68 with a total trading volume of 3.7 billion Turkish liras ($1 billion).
The U.S. dollar/Turkish lira exchange rate slightly rose to 3.6770 at 9.30 a.m. local time (0630GMT) Friday, compared to 3.6740 at Thursday’s close.