Abstract: Background - Lactate dehydrogenase (LDH) is validated prognostic marker in non-Hodgkin’s lymphoma in humans and a component of the International Prognostic Index for Diffuse Large B-cell Lymphoma. The significance of serum LDH levels in dogs diagnosed with multicentric large B-cell lymphoma is unclear. Objectives - The purpose of this study was to determine whether there was a correlation between LDH and substage. Animals – Twenty-seven dogs diagnosed with multicentric B-cell lymphoma from a veterinary hospital met inclusion criteria and were included in the study. Methods – In the prospective cohort study, LDH concentrations were measured using an IDEXX Catalyst ONE Veterinary Chemistry analyser prior to commencing CHOP chemotherapy. Group one included subjects with LDH within the reference range (40-400U/L) and group two, included those above (>400U/L). Details of clinical remission, date of cytologically confirmed disease relapse and euthanasia were recorded. Disease free interval (DFI) and mean survival time was calculated. Results – Statistical analysis showed no significant relationship between LDH levels and disease substage (p=0.396). The data indicates that LDH is not a strong predictor of disease substage in the cohort. Median DFI was higher for subjects with LDH >400U/L compared to those that were below. However, log rank test revealed that there was no statistically significant difference between the two groups (p=0.96). Conclusion - This study suggests that there is no clear correlation between LDH concentrations and substage, therefore other factors likely play a role in the biomarker metabolism. Limitations of the study included the small study population.