Two male nurses have been detained in Uruguay over dozens of suspected induced deaths at two hospitals in the capital Montevideo, police say.
They say the men - aged 49 and 36 - were held following a two-month police investigation.
The alleged killings took place in the cardiology unit of the Maciel Hospital and in the intensive care unit of the Spanish Mutual Care.
Some reports say the suspects had cited "humanitarian reasons".
The names of the two nurses - who were apparently not working together - have not been released.
Up to 50 people could have been killed through a combination of administered medication and other procedures, reports in Uruguay's media suggest.
Police inspector Jose Luis Roldan saied poison from Brazil had been used on patients who were in critical condition, the Associated Press news agency reports.
Uruguay's health ministry has so far made no public comment on the case.