Protein electrophoresis is a common proven technique to determine the protein components of plasma or serum in human, veterinary, and laboratory animal medicine. Changes in albumin and globulin protein levels can provide early and valuable diagnostic and prognostic information. Here we describe a preliminary analysis of the distribution of serum protein fractions in adult BALB/c, C57BL/6, and CD1 mice and Sprague-Dawley rats and describe the changes in protein values from birth to maturity in BALB/c mice and Sprague-Dawley rats. Quantifiable changes in the electrophoretic profile were apparent in mice with chronic-active dermatitis.