Substituted 2-(2,6-dioxopiperidin-3-yl)-phthalimides and 1-oxo-2-(2,6-dioxopiperidin-3-yl)isoindolines reduce the levels of TNF.alpha. in a mammal. A typical embodiment is 1-oxo-2-(2,6-dioxo-3-methylpiperidin-3-yl)-4,5,6,7-tetrafluoroisoindoline- .