A thin area of a slide taken from a patient who has chronic lymphocytic leukemia, which is characterized by an increased number of small lymphocytes in the bone marrow. At this power, numerous small dark cells similar in appearance to immature red cells are seen, but can be quickly confirmed as lymphocytes when viewed under oil. The actual M:E ratio is normal, since lymphocytes are not included in the final ratio. The arrows show several cell most likely representing small lymphocytes.

Some small lymphocytes are normal in the bone marrow.