A method of producing a side pocket mandrel body for use in a hydrocarbon well side pocket mandrel assembly includes providing a continuous, solid piece of material with the through-going main conduit; in the solid piece of material, forming said at least one side pocket by machining a bore, displaying an external entrance opening, into a laterally offset section of the solid piece of material generally parallel to the main conduit such that an internal wall section of the solid piece of material is brought to separate the main conduit from the machined bore; plugging the entrance opening of the machined bore with a fluid-tight plug; providing at least one opening from an outside of the mandrel body into the at least one side pocket; providing at least one opening in the wall section; and providing the solid piece of material with the first and the second connection arrangements, thereby rendering the mandrel body connectable to the up-hole and down-hole sections of the production tubing.