A metered dose aerosol actuator, for use in association with a pressurised medicament container (3) provided with a dispensing metering valve having a valve stem (4), comprising a housing (1) adapted to receive the container (3), a stem block (5), extending upwards from the base of the housing (2) and adapted to engage the valve stem (4) by means of a cavity (6) provided in the stem block (5), the stem block being provided with a spray orifice (9) adapted to be in flow connection with the valve stem (4) and the cavity, a sump (8) extending downwards from the cavity (6), relative to the spray orifice (9), wherein the sump (8) has a smooth, rounded interior surface.