At least 86 people got sick during a concert Wednesday night at Boston's TD Garden.
Officials say many of those injured were minors. Police suspect the illnesses are drug- and alcohol-related.
Some 50 people were treated on the scene, another 36 were taken to area hospitals for treatment.
The medical problems happened during a packed and steamy electronic dance concert featuring the Grammy-nominated electronic dance music DJ Avicii. Police say large incidents involving drug and alcohol problems are common at techno concerts.
"I was seeing people get dragged out. People I think on Molly and I don't know drunk. Getting out of there. Quick. Cops were very angry with them," said one concert-goer. Molly is a nickname for Ecstasy (MDMA).
"It looked like they were on drugs. Getting carried out on stretcher. People on the ground getting fought by police. A lot of stuff going on there," said another concert-goer.
"A lot of people were getting drunk of course because alcohol was being served to people who had licenses. And all I know is that some people were freaking out and they just needed to be restrained," said another witness.
Boston EMS Deputy Superintendent Mike Bosse says all of the patients' symptoms were minor. He says all of those transported and treated appeared to be between 16 and 25 years old.
Bosse blamed alcohol and drug use for Wednesday night's problems. But some concert-goers blamed oppressive heat inside the arena.
A spokeswoman for concert promoter Live Nation said early reports indicate that a majority of those taken to the hospital were people outside who were too intoxicated to be allowed inside.