In the Bay and Ensenada de La Paz there is a strong variability in the composition and abundance ofpelagic copepod species but there is no information on parasitic infection level. The early stages oftrematode is unclear because they use jellyfish, ctenophores, molluscs, chaetognaths, copepods and fish larvae as first and second intermediate hosts.The aim of this work was to study the parasitic helminths in calanoid copepods in the Ensenada de la Paz, Baja California Sur, Mexico. Zooplankton was obtainedwith a conical net of 1.5 m in length, mesh size of 300 microns and a digital flowmeter. Net tows weremade in sea surface for 5 min at 0,2 knots/h at a fixed station sampling during the last week of June 2008.Samples were fixed in formalin 4%. Copepods with parasites were sorted and identified. The extractedworms were stained with Gomori Trichome, cleared with methyl salicylate and mounte...