The health director of Takhar province said the girls fell ill shortly after drinking water at their school.
An education official in Kabul said preliminary investigations suggested the water had been poisoned.
A local official in Takhar suggested that people opposed to education for girls were responsible.
The BBC's Bilal Sarwary in Kabul says that similar events have been reported before, but no conclusive evidence of poisoning has been found.
The official said 40 girls were treated and then discharged but 100 others including female teachers have been kept in hospital, after complaining of severe nausea, headaches and dizziness.
The water has been sent to a laboratory for analysis, and the official said he had asked for a full inquiry.
A spokesman for the education directorate in Takhar said the victims are aged from 14 to 30.
He said it appeared that "narrow-minded people" opposed to education for girls were behind the incident.
More than 100 schoolgirls in northeastern Afghanistan are in hospital suffering from suspected poisoning.