Monocytosis may occur in the absence of leukocytosis. Monocytosis is most frequently found in subacute bacterial endocarditis (about 15%-20% of patients), disseminated TB (15%-20% of patients), during the recovery phase of various acute infections, in many types of hematologic disorders (including nonmonocytic leukemias, myeloma, and hemolytic anemias), in malignant lymphomas and carcinomas, in rheumatoid-collagen diseases, and in typhoid fever. Malaria and leishmaniasis (kala-azar) are frequent causes of monocytosis outside the United States. Monocytic leukemia and myelodysplastic syndromes (Chapter 7) also enter the differential diagnosis.