No cash changes hands in the impromptu exchange. The sums are transferred among the traders’ clients later.

But lately this narrow alleyway has become a microcosm of Turkish macroeconomics. While traders and some financial analysts say that Turkey is not in an economic crisis — not yet, anyway — there is a rough sense of uncertainty about the financial future.

Osman Atac, a 52-year-old currency trader known as Billiard Osman for his prowess with a pool cue, conceded that this slump in the lira was different — sharper and deeper — than others he had seen in the quarter century since he switched from selling used cars to trading money in an alley.

“We earned in ’94, we earned in 2001,” said Mr. Atac, referring to past global currency upheavals, when the lira plummeted but traders profited by arbitraging the exchange rates. But the steady, inexorable decline this time has provided fewer sharp swings that would give the traders opportunities for arbitrage.

“In this turbulence,” Mr. Atac said, “no one is making any money.”

Mr. Atac, clutching the battered Nokia cellphone he uses to keep in touch with his customers, said he thought the lira would not get any weaker than the record of 2.39 to the dollar it hit on Jan. 27. That is a sentiment shared widely in Turkey.

So far, Mr. Atac has been right. The lira has recovered somewhat since the low point, strengthening Monday to about 2.21 to the dollar, a 23 percent decline since May.

But the consequences of a further decline would be serious. Turkish companies have borrowed $130 billion in foreign currencies, according to the International Monetary Fund. Such loans offered lower interest rates, but came with a higher risk that is now materializing. When the lira goes down, it becomes more expensive for a Turkish company to make its payments on a dollar loan. If the lira weakens further, hundreds of companies could go bust.