Ghrelin stimulates proliferation of canine mammary carcinoma cells. The effect of n-octanoylated ghrelin peptide (Peptides International) and GHS-R-specific peptide antagonist [D-Lys3]-GHRP6 (Peptides International) treatment on proliferation of canine mammary cancer cells assessed by BrdU incorporation test (BD Bioscience, USA). The number of proliferating cells represented as a percentage of BrdU-positive cells (±SD) obtained with FACS Aria II (Becton Dickinson) is significantly increases after the ghrelin treatment at concentration of 1 and 10nM in CMT-W1 (A), and CMT-W1M (B) cell line whereas at concentration of 1 nM dose in CMT-W2 (C). In this cell line a decrease in number of proliferating cells after ghrelin receptor inhibitor treatment (200μM) has been observed. No significant differences has been observed in CMT-W2M cell line (D) nor after the ghrelin treatment, neither after the ghrelin receptor inhibitor treatment. The experiment has been conducted in three repetitions. The statistical analysis was performed using Prism version 5.00 software (GraphPad Software, USA). One-way ANOVA followed by Tukey HSD post-hoc test were applied. p < 0.05 was marked as *, p < 0.01 was marked as ** and p < 0.001 was marked as ***.