BACKGROUND: Vascular endothelial growth factor (VEGF), which affects tumor angiogenesis, is expressed as different splice variants, including the major isoforms VEGF165 and VEGF121, and can be cleaved by plasmin to generate VEGF110. The amount of VEGF121 and VEGF110 in biological samples has not been well studied. METHODS: We developed an ELISA that detects VEGF165 and VEGF121 equally, but does not detect VEGF110. We used this ELISA together with 2 other ELISAs, one detecting VEGF165 and the other detecting VEGF165, VEGF121, and VEGF110 equally, to assess the concentrations of VEGF121 and VEGF110 in ovarian cancer tumors. RESULTS: The median concentrations in ovarian cancer tumor lysates were 0.61 (range <0.055-74) fmol/mg protein for VEGF 165, 1.4 (range <0.20 -500) fmol/mg protein for VEGF165 plus VEGF121, and 2.3 (range <0.079 -520) fmol/mg protein for total VEGF including VEGF110 (n = 248). VEGF concentrations measured by the 3 ELISAs were highly correlated (r = 0.91-0.94). Median estimated VEGF121 and VEGF110 concentrations were 0.77 and 0.58 fmol/mg protein, respectively. In lysates with measurable VEGF165 and total VEGF concentrations, mean VEGF165 was approximately 31% (SD 23%) of the total VEGF (n = 217). In contrast, VEGF165 constituted approximately half of the total circulating VEGF. CONCLUSION: VEGF 165, VEGF121, and VEGF110 may be present at significant amounts in ovarian cancer tumors.