Phenylpyridazine compounds represented by the following formula (I): (wherein R1 represents a substituted or unsubstituted phenyl or a a substituted or unsubstituted pyridyl R2 represents a lower alkoxy group, a lower alkylthio group, a lower alkylsufinyl group or a lower alkylsulfonyl group R3 represents a hydrogen atom or a lower alkoxy group and R4 represents a hydrogen atom or a substituted alkyl group), are provided having excellent inhibitory activity against interleukin-1 beta production, and useful in the treatment of prevention of diseases caused by stimulation of interleukin-1 beta production, such as immune system diseases, inflammatory diseases, and ischemic diseases.
