The diffusion coefficient of polymers is a critical parameter in biomedicine, catalysis, chemical separations, nanotechnology, and other industrial applications. Here, measurement of macromolecular diffusion in solutions is described using a visually instructive, undergraduate-level optical refraction experiment based on Weiner's method. To reinforce concepts in polymer science, synthetic polymers and natural biopolymers are used for diffusion-coefficient measurements. The role of molecular size and conformation on the transport properties of polymers is illustrated. By changing the pH of the solution to influence the protein shape, the impact of solution environment is also demonstrated. In addition, features such as digital capture of data using a webcam, data digitization, and multivariable data regression are incorporated into the experiment to broaden the learning opportunities for students in physical chemistry, chemical engineering, and environmental and biological sciences. (Contains 1 table and 3 figures.)