Prosecutors had asked the federal court of justice to clear the two defendants, both doctors who did not intervene when their patients deliberately took fatal doses of medication.
Their actions “did not constitute a homicide”, presiding judge Norbert Mutzbauer in Leipzig said.
“If the patient kills themselves, even with help from someone else, that person's actions are not punishable under the law.”
In advance of the decision, the German Foundation for Protection of patients had told news agency DPA it would draw new lines “between permissible assisted suicide in individual cases, and forbidden killing on demand”.
While doctors in Germany may not actively kill patients, in some circumstances they can agree to patients' requests to withhold treatment, or provide treatment that provides a benefit like pain relief at the cost of shortening life.
But the sick person must be of sound mind and under no external pressure in order to legally agree to such interventions.
A lower Hamburg court had cleared one of the defendants, a neurologist and psychiatrist from the northern city.
He had certified the decisions of an 81-year-old and an 85-year-old woman to end their lives and was present when they took deadly doses of medication in 2012.
Both were suffering from multiple non-fatal illnesses that restricted their quality of life.
Meanwhile the other doctor was cleared by a Berlin court after providing a fatal drug in 2013 to a 44-year-old woman who had suffered chronic pain for almost 30 years.
He was present as she died and made no effort to prevent it.
In a “fiendishly complicated situation of conflict”, it had been his “moral duty” to help the woman, Berlin doctor Christoph T. told the federal court, appealing to the Christian injunction to love one's neighbour.
Hamburg doctor Johann Friedrich S. had urged the court to reach “a decision supporting citizens' right to make decisions about themselves.”