Abstract: The present invention relates to pyrrolidine derivatives, and more particularly to the compound (S)-1-?(S)-2-(4-methoxybenzamido)-3-methylbutyryl!-N-?(S)-2-methyl-1-(trif luoroacetyl)propyl!pyrrolidine-2-carboxamide, shown by formula I, and solvates thereof. The present invention also provides pharmaceutical compositions, intermediates and methods of preparation of the compound. The compound of formula I is an inhibitor of human neutrophil elastase and is useful in the treatment of diseases in which the enzyme is implicated, such as, for example, emphysema and acute respiratory distress syndrome (ARDS).