The much expected trial has commenced against three Dutch men charged with infecting at least 14 others with HIV virus.
The prosecution says the three promoted gay sex parties on the internet, then drugged and raped their guests and injected them with HIV-infected blood.
Twelve of the alleged victims have tested positive for HIV.
The three defendants, all HIV-positive, deny the charges, though. They face up to 21 years in prison if convicted.
They are charged with assault, rape and possession of illegal drugs.
The court, in the northern city of Groningen, heard that the three men allegedly drugged their party guests with a combination of ecstasy and a date rape drug before sexually assaulting them and injecting them with their own HIV-positive blood.
A lawyer for the alleged victims said they would launch a civil case for compensation if the defendants were convicted.
"They are hoping the trial will provide an answer to the question of why this happened to them," said the lawyer, Fred Kappelhof.