ShopKo Stores Inc. and the drugstore chain Phar-Mor Inc. have called off their proposed merger, citing continuing uncertainties in completing the transaction.

The value of the stock-swap combination was likely a factor. Before Wednesday’s announcement, Phar-Mor’s stock had lost about a third of its value from early September, when the merger was first made public. ShopKo’s stock had fallen about 8 percent as of Tuesday’s close.

“While we continue to believe that a strategic combination would make sense, it became clear that the transaction as contemplated was not likely to be completed,” said Dale P. Kramer, ShopKo’s chief executive.

He added that the “continuing uncertainty is not in the best interests of our shareholders.”

The timing was not surprising. The original deal allowed either party to walk away from the deal as of Tuesday.