Isoindolin-1-one and Isoindoline-1,3-dione substituted in the 2-position with a 2,6-dioxo-3-hydroxypiperidin-5-yl group, which may be further substituted in the 5-position with alkyl or halogeno, and in the 4-position with alkyl or a nitrogen-containing group are inhibitors of, and thus useful in the treatment of disease states mediated by, TNFα. A typical embodiment is 2-(2,6-dioxo-3-hydroxy-5-fluoro-piperidin-5-yl)4-aminoisoindolin-1-one.