Effectively teaching the concepts of osmosis to college-level students is a major obstacle in biological education. Therefore, a novel computer model is presented that allows students to observe the random nature of particle motion simultaneously with the seemingly directed net flow of water across a semipermeable membrane during osmotic simulations. Specifically, the simulations are intended to help students understand that the membrane-crossing probability of water molecules depends solely on their concentrations on both sides of the membrane. The interactive model allows for user-controlled concentration gradients and should also help students avoid some common osmotic misconceptions including those that derive from the use of teleological or anthropomorphic explanations. The model is implemented in the multiagent NetLogo environment and is accessible as a platform-independent Java applet. (Contains 1 figure.)