A modified agyrophil technique was applied to peripheral blood smears to determine the mean AgNOR counts (MAC) of lymphocytes and ultimately assess the state of the lymphoid system in various clinical conditions of dogs. Fifty dogs, from clinically normal to pets with leukaemia, presented to the Veterinary Teaching Hospital, were recruited. Blood smears from each dog were stained with routine Romanowsky and modified agyrophil stains. Signalment, clinical diagnoses and hematologic parameters of the dogs were related to the MAC. An AgNOR proliferative index (AgPI) — percentage of lymphocytes with 3 or more AgNORs, was determined, and correlated with MAC. The statistical significance was determined at P < 0.05. MAC ranged from 1.17 in clinically healthy patients to 6.00 in leukaemic patients. The MAC was 2.00 in patients (n = 26) with lymphocyte counts within reference intervals (900—2400 per microliter); 2.23 in patients (n = 4) with lymphopenia; 2.18 in patients with lymphocytosis (n = 18) and 4.73 in patients (n = 4) with lymphocytic leukemia. Also, the MAC was 2.00 in non-anemic dogs while it was 2.47, 2.49 and 3.06 in patients with mild, moderate and severe anaemia, respectively. The MAC correlated strongly with AgPI (r = 0.91). The ancillary AgNOR technique provides a cheaper, more rapid and sensitive tool than routine lymphocyte counts in assessing the state of lymphoid proliferation in a variety of conditions in the dog.