A marking instrument, for applying a fluid to a surface and particularly, though not exclusively, to a writing pen, including a marker pen, or a brush, especially an artist's brush. Other types of brushes are contemplated, such as those for applying cleaner, mouthwash or perfume to teeth. The instrument (2) comprises a tip (6) a holder for the tip (4), a cartridge (14) containing the fluid mounted within or connectable to the holder (4), and a manually-operable spray pump arrangement (10) for repeatedly dispensing a predetermined amount of the fluid under pressure from the cartridge (14) to the tip (6) of the instrument (2). A disposable or refillable cartridge for the instrument is also described.