Introduction Hypertension is a major risk factor for cardiovascular and chronic kidney disease. However, its causes remains unclear in most cases. Our recent data suggests that macrophages contribute to, and protect from, hypertension by regulating the endothelin (ET) system [Czopek, Eur Heart J 2019]. ET-1 is the most potent endogenous vasoconstrictor with pro-inflammatory properties. We have shown that macrophage remove ET-1 through the ETB receptor (ETBR). As cardiovascular risk varies between men and women, here we explored if the expression of the ET system and ET-1 clearance varies between male and female mice and with macrophage phenotype. Method Bone marrow derived macrophage from 9–12 weeks old male (n=5) and female (n=7) C57B6J mice were cultured in vitro. LPS/IFNγ were used to polarise macrophage to a pro-inflammatory/M1 phenotype and IL-4/IL-13 for anti-inflammatory/M2 polarisation. Gene expression was determined using qPCR. ET-1 concentration was measured by ELISA. Macrophage were then exposed to 2 ng/mL fluorescently-labelled ET-1 (fET-1) and the concentration was measured by fluorescence spectrophotometry after 12 hours. Statistical analyses were performed using a two-way ANOVA with Sidak’s multiple comparison method. Results Unstimulated macrophagesMale macrophage expressed 2-fold greater ETBR than females (p<0.01). There was no difference in ppET-1 expression between the sexes. Neither male nor female macrophage showed net production of ET-1. Whereas, male macrophage cleared all extracellular ET-1, females cleared none (p<0.05). Polarised macrophages Both male and female macrophage expressed ETBR and ppET-1. Whereas ETBR levels were similar, male macrophage displayed 3-fold greater ppET-1 than females (p<0.05). Net ET-1 production was similar between male and female macrophage (∼20 pg/mL at 24 h). However, male macrophage cleared extracellular ET-1 whereas females did not (p<0.05). Both male and female macrophage expressed ETBR and ppET-1 similarly. Neither males nor females demonstrated net ET-1 production or ET-1 clearance. Conclusions Our data suggest a sex difference in ET system expression and in ET-1 clearance by macrophage. The increased clearance seen with male macrophage is consistent with increased ETBR expression relative to female macrophage. These differences may be important in the cardiovascular risk difference observed between men and women.