AIM Semaphorin 3A urinary levels represent an early, predictive biomarker of acute kidney injury and positively correlate with albumin-to-creatinine ratio and serum creatinine in hypertensive patients with chronic kidney disease. Our purpose has been to evaluate semaphorin 3A serum levels in a cohort of haemodialysis (HD) patients, the influence of a single HD session on its concentrations, and the potential correlation with clinical and biochemical parameters. METHODS We enrolled 18 patients receiving HD with Acetate-Free Biofiltration technique and 16 healthy subjects as controls. Peripheral venous blood samples were obtained from patients at different intervals: start of dialysis (pre-HD), middle, and end of the treatment (post-HD). We also collected dialysate samples by the Quantiscan monitoring system (Hospal, Bologna, Italy). RESULTS Semaphorin 3A was significantly lower in HD patients at baseline compared to controls (median 19.50 (interquartile range 1.00-65.00) versus 97.50 (23.50-161.00) ng/mL, P = 0.0237). A statistically significant reduction was seen during a single HD session (from 19.50 (1.00-65.00) to 0.86 (0.82-4.21) ng/mL, P < 0.0001), with a reduction ratio of 65.92 ± 33.51%. The median concentration in dialysate was 54.00 (15.00-102.00) ng/mL. Pre-HD values were directly related to serum vitamin D (r = 0.872; P = 0.001) and inversely correlated with calcium levels (r = -0.426; P = 0.012) and calcium × phosphate product (r = -0.422; P = 0.0252). CONCLUSION Semaphorin 3A removal during HD may be clinically relevant due to its involvement in different aspects of cell physiology and in bone remodelling. Semaphorin 3A both inhibits osteoclastic bone reabsorption and increases osteoblastic new bone formation, thus playing a dual osteoprotective role.