We previously reported that lysophosphatidic acid (LPA) represents a potential biomarker for ovarian and other gynecologic cancers. To further improve the accuracy and potentially increase the sensitivity and specificity of the assay, we developed an electrospray ionization mass spectrometry (ESI-MS)-based method to analyze LPA and related lysophospholipids. LPA, lysophosphatidylinositol (LPI), lysophosphatidylserine (LPS), and lysophosphatidylcholine (LPC) could be detected with high sensitivity (in low pmol range) using this method. Standard curves were established for quantitative analysis. LPA and closely related lysophospholipids isolated from thin-layer chromatography (TLC) plates were analyzed directly by ESI-MS. This ESI-MS-based assay allows simultaneous detection and quantitation of all different species of LPAs and LPIs in a sample over a range of at least 5-300 pmol. Moreover, this test was at least 50 times more sensitive when a multiple reaction monitoring (MRM) mode was used. Using these protocols in a limited set of analysis, we found that both LPA and LPI were elevated in patients with ovarian cancer.