Police here are hunting a small group of fans of FC Cologne who are believed to be responsible for throwing cups of urine and faeces at rival supporters during a German league match last weekend.
According to security staff at Schalke's stadium in Gelsenkirchen, a small group of Cologne ultras are responsible for throwing the cups during the home team's 5-1 win.
Those hit by the disgusting missiles included fans from both teams.
Police are looking at video tapes of the crowd from Saturday's match at Schalke's Veltins Arena to identify those responsible and two fans are reported to have already been arrested.
A witness is reported to have seen one man put faeces in a beer cup, while two others filled their cups with urine before hurling them at Schalke fans.
Cologne president Wolfgang Overath has expressed shock at the behaviour of his club's fans and condemned their behaviour.
"These are not football fans, these people have no interest in sport and have no business being in the stadium," he told SID, an AFP subsidiary.
"It is hard to believe that football is being abused by such behaviour.
"The German Football Federation (DFB) and the club must think about what could lead to such excessive behaviour."
A Cologne supporters' spokesman called for those responsible to be banned.
"This is totally unacceptable and there can be no excuse," said Rainer Mendel, who revealed two fans have already been arrested.
"The perpetrators must be punished and banned from the stadium."
According to a report by Cologne evening newspaper Die Koelnische Rundschau, a group of Cologne fans pelted police with bottles and other dangerous objects before Saturday's game.
Officers responded by using batons and pepper spray to calm the situation.