The aim of this study is to investigate the usability of serum procalcitonin level in dogs as a clinical biomarker for the distinction between bacterial, viral, and parasitic diseases. A total of 160 dogs were used. The animals were evaluated in four groups as control and those with bacterial, viral, and parasitic infections. Serum procalcitonin, tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta ( IL-1 beta), interleukin-6 (IL-6), interferon-gamma (IFN-gamma) level, and total white blood cell (WBC), and differential leukocyte count were determined. Serum procalcitonin level was found to be higher in dogs with bacterial infection compared to the control group and dogs with viral disease (P = 0.019). It was observed that serum procalcitonin level in dogs with bacterial infection varies related to the disease agent and it was found higher in those with pyometra (P = 0.009). Serum procalcitonin level was higher in dogs which had parasitic infections but, the difference is not significant. IL-6 level was found higher in dogs with viral and parasitic diseases than those in the control ( P = 0.006). A negative correlation was determined between procalcitonin and IFN-gamma (P = 0.001). While a positive correlation was detected between procalcitonin and WBC count, a negative correlation was determined between procalcitonin and monocyte percentage. In conclusion, serum procalcitonin level can be used as a clinical biomarker in bacterial diseases and, perhaps, in some parasitic diseases in dogs. However, further studies should be conducted to determine threshold values that take the severity of infection, its prevalence, and clinical course into account.