Systemic mastocytosis is characterized by bone marrow involvement, which requires a bone marrow biopsy for diagnostic work-up. We questioned whether bone marrow involvement could be predicted using biochemical markers. We selected patients with various symptoms suggestive of indolent systemic mastocytosis, of whom 63 ultimately had bone marrow involvement. Patients suspected of aggressive mastocytosis, or mastocytosis associated with other hematologic diseases were excluded. Evaluation of 115 patients and 15 patient controls demonstrated a test accuracy for serum tryptase, urinary N(-) methylhistamine and N(-) methylimidazole acetic acid of 96%, 88% and 95% respectively. These markers provide an excellent pre-test probability of indolent systemic mastocytosis.