The lacrimal drainage system drains fluid that exists normally on the surface of the eye into the nasal cavity. This paper describes a hand-held, personal-computer-based instrument to quantitatively estimate the resistance to fluid flow through the lacrimal drainage system. This resistance measurement is proposed as a possible means to diagnose blockage of the system and to verify the degree of change in resistance after clinical treatment. The instrument system consists of a hand-held syringe attached to pressure and flow transducers. Resistance is calculated as the ratio of differential pressure to flow rate and is displayed in real time on a computer monitor.