Grey Bruce OPP are investigating a four-vehicle collision north of Mount Forest.
Provincial police and Guelph-Wellington Paramedic Service were called to the scene on Highway 6, south of Southgate Road 8 around 6:37 p.m. Monday.
A transport truck, two sedans, and an SUV were all involved.
One of the sedan drivers was seriously hurt. The other sedan driver and the driver of the SUV suffered non-life threatening injuries. The transport truck driver was not hurt.
Highway 6 reopened around 6 a.m. today.