The aim of the study was to compare the relative gene expression of Haemonchus contortus P-glycoprotein genes ( Hco-pgp ) between fourth (L 4 ), infective (L 3 ), and transitory infective (xL 3 ) larval stages as laboratory models to study ivermectin (IVM) resistance. The H. contortus resistant to IVM (IVMr) and susceptible to IVM (IVMs) strains were used to develop xL 3 in vitro culture and to infect Meriones unguiculatus (gerbils) to collect L 4 stages. Morphometric differences were evaluated from 25 individuals of H. contortus from each strain. Relative gene expression from xL 3 and L 4 was determined between comparison of IVMr stages and from IVMr vs IVMs stages. Seven Hco-pgp genes (1, 2, 3, 4, 9, 10, and 16) were analysed by RT-qPCR using L 3 stage as control group, per strain, and GAPDH and β-tubulin as constitutive genes. Morphological changes were confirmed between xL 3 and L 4 developing oral shape, oesophagus, and intestinal tube. In addition, the body length and width showed statistical differences ( p < 0.05). The Hco-pgp 1, 2, 3, and 4 genes ( p < 0.05) were upregulated from 7.1- to 463.82-fold changes between IVMr stages, and Hco-pgp9 (13.12-fold) and Hco-pgp10 (13.56-fold) genes showed differences between L 4 and xL 3 , respectively. The comparative study between IVMr vs IVMs strains associated to xL 3 and L 4 displayed significant upregulation for most of the Hco-pgp genes among 4.89-188.71 fold-change. In conclusion, these results suggest the use of H. contortus xL 3 and L 4 as suitable laboratory models to study IVMr associated with Hco-pgp genes to contribute to the understanding of anthelmintic resistance.