The present invention relates to a closure for filling and sealing receptacles containing medicinal fluids, a method for filling a receptacle with a medicinal fluid and sealing the receptacle. The closure used in the method comprises a mounting piece that may be attached to the receptacle and a connector piece that may be connected to a connector piece of a filling device. A closure body is arranged between the mounting piece and the connector piece, in which a closure piece for sealing the closure sits. The closure piece may be slid between a position sealing the closure and a position which opens the closure. The closure is sealed tight with a removable protective cap. The present method is characterized in that with the protective cap removed the receptacle is filled through the closure in a clean room, whereupon after filling, the closure is sealed by pressing the closure piece into the closure.