The present invention relates to particular forms of a novel 1-substituted-N-\x9b2-methyl-1-(trifluoroacetyl)propyl!pyrrolidine-2-carboxam ide which are inhibitors of human leukocyte elastase (HLE), also known as human neutrophil elastase (HNE), making them useful whenever such inhibition is desired, such as for research tools in pharmacological, diagnostic and related studies and in the treatment of diseases in mammals in which HLE is implicated. The invention also includes pharmaceutical compositions containing such forms, processes for preparing the forms and intermediates useful in the synthesis of the forms.