Lysophospholipids such as lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), and lysophosphatidylserine (LysoPS) are attracting attention as second-generation lipid mediators. We have pursued the clinical introduction of the assays of lysophospholipids and related proteins, and in this review, the clinical application of the assay of LPA and autotaxin(ATX), which produces LPA from lysophosphatidylcholine through its lysophospholipase D activity, is mainly described. The assay of ATX is promising as a useful laboratory test, especially for the diagnosis and staging of liver fibrosis