A method of producing a side pocket mandrel body for use in a hydrocarbon well side pocket mandrel assembly, which side pocket mandrel body comprises: - a first end displaying a first connection arrangement for connecting the side pocket mandrel body to an up-hole section of a production tubing of the hydrocarbon well, and a second end displaying a second connection arrangement for connecting the side pocket mandrel body to a down-hole section of the production tubing, - a longitudinal, through-going main conduit for communicating with a central passageway of the production tubing, and - a side pocket section comprising at least one side pocket for retrievably housing an injection fluid flow control device, which method comprises the steps of: - providing a continuous, solid piece of material comprising the through-going main conduit, - in the solid piece of material, forming said at least one side pocket by machining a bore into a laterally offset section of the solid piece of material, said bore being 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,said bore displaying an external entrance opening, - plugging the entrance opening of the machined bore with a fluid-tight plug, - providing at least one opening from an outside of the side pocket mandrel body into the at least one side pocket, thereby forming an injection fluid inlet, - providing at least one opening in the wall section, thereby forming an injection fluid outlet, - providing the solid piece of material with the first and the second connection arrangements (3, 5), thereby rendering the side pocket mandrel body connectable to the up-hole and down-hole sections of the production tubing, - forming a recess within the side pocket mandrel body by machining the inside of the main conduit removing material internally from said solid piece of material, and - bringing the recess to communicate with said at least one side pocket, thereby rendering the at least one side pocket accessible from the main conduit via the recess. - a first end displaying a first connection arrangement for connecting the side pocket mandrel body to an up-hole section of a production tubing of the hydrocarbon well, and a second end displaying a second connection arrangement for connecting the side pocket mandrel body to a down-hole section of the production tubing, - a longitudinal, through-going main conduit for communicating with a central passageway of the production tubing, and - a side pocket section comprising at least one side pocket for retrievably housing an injection fluid flow control device, - providing a continuous, solid piece of material comprising the through-going main conduit, - in the solid piece of material, forming said at least one side pocket by machining a bore into a laterally offset section of the solid piece of material, said bore being 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,said bore displaying an external entrance opening, - plugging the entrance opening of the machined bore with a fluid-tight plug, - providing at least one opening from an outside of the side pocket mandrel body into the at least one side pocket, thereby forming an injection fluid inlet, - providing at least one opening in the wall section, thereby forming an injection fluid outlet, - providing the solid piece of material with the first and the second connection arrangements (3, 5), thereby rendering the side pocket mandrel body connectable to the up-hole and down-hole sections of the production tubing, - forming a recess within the side pocket mandrel body by machining the inside of the main conduit removing material internally from said solid piece of material, and - bringing the recess to communicate with said at least one side pocket, thereby rendering the at least one side pocket accessible from the main conduit via the recess.