a closure cap for infusion and transfusion bottles having a rim cap which grips around a rim neck of a bottle and has a cutout which is closed by a plastic lid so that an annular zone of the plastic lid grips below the edge of the cutout to obtain a tightly sealed attachment of the lid this attachment can nevertheless be lifted off with relatively little force due to a radially extending intended - bend line of the plastic lid formed by a thinning of the material .