3-Carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) is a metabolite of furan fatty acids found in plasma and urine of humans after consumption of foods containing these fatty acids. Recently, CMPF has been identified as a prominent metabolite following the consumption of either fish oil, fish oil fatty acid-ethyl esters or diets rich in fish. As furan fatty acids are known to occur in fish and fish oils (at a low level), it is possible that in these studies the CMPF in plasma originated from furan fatty acids. We report the plasma CMPF levels in 10 healthy women who consumed 1 gram of pure eicosapentaenoic acid (EPA), or docosapentaenoic acid (DPA) or docosahexaenoic acid (DHA), or olive oil daily for 6 days, in a cross-over study. The supplemented omega 3 fatty acids contained no detectable levels of furan fatty acids. The plasma CMPF and omega 3 fatty acid levels were measured by LC-MS/MS. Consumption of pure omega 3 fatty acids led to a significant increase in the plasma CMPF levels, but not with olive oil (from 1.6 to 2.5-fold compared with baseline). The plasma free fatty acid levels of EPA, DPA and DHA also increased significantly when they were supplemented (p < 0.05). Significant positive correlations existed between the plasma free fatty acid DPA and DHA levels (p < 0.05 and r = +0.49 to +0.81), but not between the EPA and CMPF levels. These data suggest that purified long chain omega 3 fatty acids may be precursors of CMPF; however the metabolic pathway(s) from omega 3 fatty acids to CMPF remain to be elucidated.