It is important for students to be exposed to the concept of osmotic pressure. Understanding this concept lays the foundation for deeper discussions that lead to more theoretical aspects of water movement associated with the concepts of free energy, water potential, osmotic potential, pressure potential, and osmotic adjustment. The concept of osmotic pressure is usually taught through lecture, without opportunities for hands-on experiences, and if experiences are provided, they rarely have quantitative measurements associated with them. Studying osmotic pressure with hands-on, inquiry-based experiments may allow students to more fully appreciate and comprehend this important concept, as well as reinforce the basic principles of water movement across membranes. Many biology classrooms may already be equipped with most of the necessary instrumentation to make measurements of osmotic pressure, or the teachers may be able to borrow it from their colleagues in chemistry or in physics. What the teachers lack is a simple, inexpensive osmometer that can be attached to that existing equipment. In this article, the authors describe a simple membrane osmometer made from readily-available items. They present a step-by-step procedure for making this membrane osmometer as well as directions for filling it with test solution. They also present descriptions and discussions of some basic experiments that use the device. (Contains 7 figures and 1 table.)