Canine malignant lymphoma is one of the most common malignant tumours occurring in dogs. Most dogs with malignant lymphoma are characterized by painless peripheral lymphadenopathy. Nonspecific signs of systemic involvement include; lethargy, anorexia, fever, anaemia and weight loss. The mean age of dogs with malignant lymphoma varies from 6.3 to 7.7 years, with no obvious gender predilection. The purpose of this study was to describe in detail clinical features, the haematological and blood serum biochemistry as well as the thymidine kinase activity in canine malignant lymphoma in order to facilitate early diagnosis. Based on cytopathological analysis, canine malignant lymphoma was diagnosed in 20 dogs (11 males and 9 females). The animals' age ranged from 3 to 12 years (median 7.6 years). In 35% of the dogs, regional or general lymphadenopathy was the only clinical sign. In the remaining cases, at least one abnormality connected to canine malignant lymphoma was found. Between ill and healthy dogs, a p-value of < 0.001 was calculated for the haematological parameters: red blood cell count, haemoglobin, haematocrit, platelet, neutrophils and monocytes; for biochemical parameters the following p-values were calculated: blood urea nitrogen P< 0.01; aspartate aminotransferase, alkaline phosphatase and thymidine kinase (TK) P< 0.001, and Calcium P< 0.05. The study results show that in medium and advanced-aged anaemic dogs with non-specific clinical features but at least one enlarged lymph node and elevated ALP and TK concentrations, canine malignant lymphoma must be considered as a possible cause.