Five Northwestern students were drugged and three of them sexually assaulted at on-campus fraternity housesSome of the alleged attacks took place at Sigma Alpha Epsilon's chapter on January 21 and were reported to the university's Sexual Harassment Prevention Office last Thursday.
Four girls fear they were date raped at the event and two say they were sexually assaulted after being given drugs.
Another anonymous report alleges that a fifth girl was drugged and sexually assaulted at another fraternity house on February 2.
Northwestern issued a security alert in light of the allegations on Tuesday. It's not clear who reported the claims to university officials.
'On January 21, 2017, four female students attending an event at the Sigma Alpha Epsilon fraternity house in Evanston were possibly given a date-rape drug.
'The report alleges that two of the students believe they were also sexually assaulted.
'In addition, on February 3, 2017, the University received an anonymous report alleging that on February 2, 2017, a female student was sexually assaulted, possibly involving use of a date-rape drug, after attending an event at another fraternity house.
'The report is unclear as to where the assault may have occurred.
'The University's Sexual Harassment Prevention Office is conducting an inquiry into these reports, and anyone with knowledge of these alleged incidents is urged to contact the Title IX Coordinator,' a statement released on Tuesday said.
No one from the university would comment further as the investigation continued on Tuesday morning.
It's not clear how old any of the students involved are.
Sigma Alpha Epsilon's national chapter said it was investigating the allegations.
'The Sigma Alpha Epsilon headquarters has launched an investigation into a sexual-assault allegation regarding our chapter at Northwestern University.
'In addition, we will be working with university administrators and chapter leaders to gain more information on the incident, and our staff member specifically assigned to Title IX matters will be working with our investigative team.
'Any form of assault or sexual misconduct by anyone, brother or not, college man or not, is completely unacceptable, and we do not tolerate actions that are inconsistent with our mission,' spokesman Brandon Weghorst told DailyMail.com.
Its Northwestern chapter president did not immediately responded to the allegations.
S.A.E. was re-named ''sexual assault expected' by female students across the country in The Hunting Ground, a widely acclaimed 2015 documentary which shed light on the epidemic of campus rape and attacks in the US.
The fraternity's headquarters said the label was 'an unfortunate stereotype'.
'Our members pride themselves on being gentlemen and leaders in their community... when we have individuals who deviate from our values, we take disciplinary action,' Mr Weghorst added.
S.A.E.'s Yale chapter was forced to admit it had violated the university's sexual misconduct policy during a 2014 initiation ceremony.
It was temporarily banned from taking part in university events as a result of the breach, details of which were never fully made public.
The Yale chapter was also once accused of turning black female students away from parties where brothers were falsely accused of telling them: 'White girls only'.
No evidence of such treatment was found in a university investigation.
The fraternity also had its housing privileges revoked by Stanford University in 2014 after a scathing report found it had created a 'hostile' environment for female students which breached the school's sexual harassment code.
Its brothers have also been caught up in racism scandals at other schools.
Students at the University of Oklahoma were expelled in 2015 after being filmed singing a racist chant en route to a party.
The fraternity was permanently excluded by Oklahoma University as a result.
An investigation later revealed that the song, which referenced lynching and taunted black students as to why they would never be accepted in to its fold, was used at five other chapters.
Other members have died while taking part in booze-fueled initiation rituals.
The hazing was eventually banned by the fraternity's national chapter.
'Five female Northwestern students were drugged and three were sexually assaulted at on- campus fraternity houses' Jennifer Smith Dailymail.com 7 February 2017