In a clinical setting, especially with species of special interest, it is important to use all clinical pathology testing options for general health monitoring and diagnosis. Protein electrophoresis (EPH) has previously been shown to be an important adjunct tool in veterinary medicine. Serum samples from 18 free-ranging and 12 zoo-based koalas (Phascolarctos cinereus) were subject to EPH analysis. Significant differences were found between the two groups for the following values: total protein, albumin, β globulins, and albumin-globulin ratio (P < 0.05). By using the combined data, the minimum–maximum values for the EPH fractions were as follows: total protein 5.0–7.8 g/dl, albumin 2.8–4.7 g/dl, α-1 globulins 0.5–1.1 g/dl, α-2 globulins 0.3–0.7 g/dl, β globulins 0.4–1.0 g/dl, γ globulins 0.2–1.0 g/dl, and albumin-globulin ratio 1.0–2.1.