Abstract: The invention relates to an adjustable-volume metering pump automatic dispenser of sanitary products for toilet water cisterns, made up of a reservoir and of an auxiliary reservoir, and in which: the reservoir contains a sanitary product and an adjustable-volume metering pump of a membrane-pump version is mounted by a sealed assembly in its lower part, and each time the toilet is used, the auxiliary reservoir releases the dose of sanitary product into the water at the end of the flush and then receives from the adjustable-volume metering pump a new dose of sanitary product required for the next use of the toilet.