N-[1-oxo-2-alkyl-3-(N-hydroxyformamido)-propyl]-(carbonylamino-aryl or -heteroaryl)-azacyclo.sub.4-7alkanes or thiazacyclo.sub.4-7alkanes or imidazacyclo.sub.4-7alkanes have interesting properties, e.g., in the treatment or prevention of disorders amenable to treatment by peptidyl deformylase inhibitors such as treatment of bacterial infections.