This paper will discuss the case of a 9 year old male castrated Golden Retriever which presented to the oncology service on 7/12/04 with a referral for non-painful superficial lymphadenopathy, prolapsed left nictitating membrane, and intermittent upper respiratory stridor. He originally presented to the rDVM on 6/21/04 for non-painful superficial lymphadenopathy, and was diagnosed on fine needle aspirate (FNA) with presumptive reactive (inflammatory) lymphoid hyperplasia. He returned to rDVM on 6/25/04 with same clinical signs, as well as, a prolapsed nictitating membrane on his left eye. Repeat FNA of, at this time, a different node still suggested reactive lymphoid hyperplasia. Three weeks on systemic and ophthalmic ointments did not resolve the clinical signs, so he was referred to Cornell University for a referral for possible Lymphoma. On 7/12/04, he was worked up for presumptive lymphoma. Physical exam revealed the same clinical signs previously described, as well as, tonsillar enlargement and two subcutaneous masses. A critical factor in the initial diagnosis was the CBC. It showed evidence of possible myeloid leukemia (blasts in circulation). The main focus of the case presentation will be on explaining the terminology used to describe Lymphoma and Leukemia. This will help to understand the logic behind the procedures employed to reach a definitive diagnosis.