The invention relates to a dispenser for delivering portions of liquid to pasty substances, having a storage container and a pumping chamber, the pumping chamber having at least one valve, and having a delivery head which can be displaced relative to the storage container and the displacement of which allows the substance to be delivered, the delivery head further having formed in it a delivery channel with a delivery opening, which delivery opening can be closed by a closure part which is removable, but is held in captive fashion on the delivery head. In order to specify such a dispenser for delivering portions of liquid to pasty substances which is configured in an advantageous manner, in particular, in respect of a closure part, it is proposed that the closure part is a sliding part which also forms a delivery-channel portion and interacts with a fixed closure pin.