The present invention relates to certain novel heterocyclic ketones which are 1-pyridylacetamide ketones of formula I, set out herein, 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 intermediates useful in the synthesis of these heterocyclic ketones, processes for preparing the heterocyclic ketones, pharmaceutical compositions containing such heterocyclic ketones and methods for their use.