The invention provides a method capable of readily discriminating pathologic conditions and judging selection of a therapeutic drug, the degree of the therapeutic effect, discontinuation of medication, etc., wherein stages quantitatively judged by digitizing substances contained in urine, which is different from conventional methods for judging stages of an interstitial pneumonitis which are performed by observation of mucous lesions with endoscopy requiring the skill or by analysis of histological samples collected from the living body. The method measures the value of main metabolites of prostaglandin E (PGE-MUM) concentration in urine and judges stages between the pre-remission phase of interstitial pneumonitis.