Mast cells are tissue‐resident immune cells derived from CD34⁺ progenitor cells in the bone marrow. Mast cells are thought to be present within most Ɵssues of the body, although their overall distribution is still not fully understood. Flow cytometry was used to assess the prevalence of mast cells in the urinary bladder, small intestine and the lungs in C57BL/6J mice. CD45.2, CD117, CD34, and FcεRIα antibodies were used to identify mast cells. Preliminary data suggests that CD117+CD34+FcεRIα+ mast cells constitute 4.30% of all CD45.2+ haematopoietic cells in the urinary bladder (n=6), 3.24% in the small intestine (n=6) and 0.11% in the lungs (n=6). This suggests that mast cells constitute a greater proportion of haematopoietic cells within the urinary bladder, and a lower proportion of haematopoietic cells in the lungs. This data will be used to further the current understanding towards the distribution of mast cells within these organs. Further studies in this area may also facilitate an enhanced understanding of how the systemic distribution and prevalence of mast cells changes during inflammatory diseases.