Drugs applied on human cancer cells can influence the rate of cell proliferation. The present study investigates the use of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide (MTT) colorimetric assay to evaluate canine tumor cell proliferation after exposure to the injectable anesthetic, propofol. Primary (CIPp) and metastatic (CIPm) canine tubular adenocarcinoma cell lines were incubated with cell culture medium (control) or propofol (1, 5, and 10 μg/mL). The MTT assays were performed after 6 and 12 hours of exposure. Measurements of absorbance were obtained for each condition with a spectrophotometer and compared with controls using a 3-way analysis of variance (P < 0.05). An increased cell proliferation rate was observed in CIPp exposed to 5 and 10 μg/mL of propofol for 6 hours and 1, 5, and 10 μg/mL for 12 hours. No significant changes were observed in CIPm after 6 hours of exposure. All propofol concentrations decreased the cell proliferation rate in CIPm after 12 hours of exposure. The MTT assays showed that exposure of CIPp to propofol for 6 and 12 hours increased cell proliferation. A decrease in the CIPm proliferation rate was observed when propofol exposure lasted for 12 hours. Further studies are warranted to better understand the role of propofol on cancer cell proliferation.