It is alleged that civil servants were among those who profited from the purchase of blood supplies imported from abroad throughout the 1990s.
On Wednesday 14 people were arrested in three Brazilian cities.
The darkly named Operation Vampire has revealed fraud said by the Brazilian government to total $637m.
The money was allegedly siphoned off by civil servants and others involved in the state purchase of blood supplies used to treat haemophilia.
Suspicion from 1990 until 2002 Brazil's department of health was buying the supplies from abroad for a fixed price of 41 US cents per unit.
That figure seemed suspiciously high to the country's new government, which launched an investigation after taking office last year.
Those detained include businessmen and civil servants, among them a senior accountant from the department of health.
Exact details of the investigation are still emerging.
But the allegation seems to be that government employees were buying blood at one price, invoicing the state for a higher amount and profiting from the difference.
Announcing details of the arrests, Brazil's justice minister said he was committed to fighting corruption whether it occurred inside or outside government.