Abstract: Disclosed are compounds, compositions and methods for inhibiting interleukin-1.beta. (1L-.beta.) protease activity. The compounds, N-(pyrimidinyl)-aspartic acid .alpha.-substituted methyl ketones and aspartic acid aldehydes, have the formula (I) set out herein.These compounds are inhibitors of 1.beta.-converting enzyme and as such are useful whenever such inhibition is desired. For example, they may be used as research tools in pharmacological, diagnostic and related studies and in the treatment of diseases in mammals in which IL-.beta. protease activity is implicated.