Phosphodiesterase type 4 (PDE 4 ) inhibitors are currently being evaluated as potential therapies for inflammatory airway diseases. However, this class of compounds has been shown to cause an arteritis/vasculitis of unknown etiology in rats and cynomolgus monkeys. Studies in rodents have demonstrated the anti-inflammatory effects of PDE 4 inhibitors on lipopolysaccharide (LPS)-induced airway inflammation. The aim of this work was to assess the direct effects of PDE 4 inhibitors on inflammatory cells and cytokine levels in the lung in relation to therapeutic effects. The effects of the PDE 4 inhibitors 3-cyclopropylmethoxy-4-difluoromethoxy-N- [3,5-di-chloropyrid-4-yl