The talks, which lasted 3Ѕ hours, were a prelude to a potentially decisive face-off Monday between Schroeder; Merkel; the chairman of Schroeder's Social Democratic Party, Franz Muentefering; and Merkel's fellow conservative leader, Edmund Stoiber.
Schroeder and Muentefering were seen leaving the meeting site, across from the Reichstag parliament building, but stayed well away from waiting reporters. Merkel left shortly after that, also saying nothing publicly.
While both sides acknowledge the need to press ahead with forming a government that can tackle the country's high unemployment and economic stagnation, neither has wanted to be seen hurrying to give way on its claim to the chancellery.
The four leaders, who had already spent four hours together on Thursday, so far have stuck to a pledge to make no public disclosures about their negotiations until they have party approval. Muentefering said the results of Sunday night's meetings would be taken to the party leaderships Monday morning, after which the four would hold another round of closed-door talks.
Party leaderships will then meet again, and only then will it be clear "whether (formal coalition) negotiations can begin, yes or no," he told reporters on the sidelines of a labor conference.
In several rounds of exploratory talks, the two parties have nevertheless identified a string of fields where they believe they can work together, including reforming Germany's tangled federal system and shoring up the government's overdrawn finances, AP reports.