1. The coelomocytes of eleven species of holothurians, representing four orders, were surveyed and described. Eight of these species have not before been surveyed for their coelomocyte contents. 2. The results of the investigation indicate that holothurian coelomocytes fall into five basic categories: hemocytes, amoebocytes, morula calls, lymphocytes, and crystal cells. 3. Brown bodies do not represent a separate coelomocyte type, but are normally found in holothurian coelomic fluid. 4. Amoebocytes, lymphocytes, and morula cells are believed to be present in the coelomic fluid of all holothurians. Hemocytes appear to be limited mainly to certain groups of the orders Dendrochirota and Molpadonia. Crystal cells have not yet been observed in order Apoda. 5. Any coelomocyte type present in a given species may be found in any of the coelomic compartments, with the exception of the hyponeural sinuses in which coelomocytes have not yet been observed.