This chapter describes the practical aspects of performing cytogenetic studies in a variety of lymphoid disorders, including the lymphomas, multiple myeloma, chronic lymphocytic leukemia, and other chronic lymphoproliferative diseases. They are also required for studies of acute lymphoblastic leukemia of mature T-cell or B-cell types. As mentioned in the previous chapter, most lymphoid cells are either T-lineage or B-lineage. During normal differentiation, they become capable of responding to antigens, and one of these responses is to transform and undergo division. A variety of reagents (known as mitogens) with antigenic properties are used in the laboratory to stimulate the cells to transform in a similar way. The two mitogens featured in the methods described here are Phytohemagglutinin (PHA) for T-cells (see Note 1), and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) for B cells. Other B-cell mitogens are described in Note 2. Be aware that no mitogen is absolutely specific to T cells or B cells (see Note 3).