*Some causes of peripheral blood plasmacytosis.* *Reactive* - Bacterial and viral infections and immunisation - Hypersensitivity reactions to drugs - Streptokinase administration - Serum sickness - Systemic lupus erythematosus *Neoplastic* - Multiple myeloma and plasma cell leukaemia - Gamma heavy chain disease - Waldenström macroglobulinaemia (rarely) - Angioimmunoblastic T‐cell lymphoma