<p>Disclosed is a method for diagnosing or detecting fibromyalgia by using a specific peptide in blood as an indicator. Also disclosed is a method for evaluating or assessing a medicinal agent for fibromyalgia effectively by using the peptide as an indicator. Serum collected from a fibromyalgia patient is subjected to peptide analysis by using a peptide which shows a specific expression level in the blood collected from the patient as an indicator (a biomarker) for fibromyalgia. This method is highly useful as a method for diagnosing or detecting fibromyalgia or evaluating or assessing a medicinal agent for fibromyalgia.</p>
