Closed suction drains remain in widespread use in surgical practice. There have been reports of complications associated with their use. We sought to characterize the pressure-generating capacities of three commonly used closed suction drainage systems. Three commonly used closed suction surgical drainage systems were studied: Davol Reliavac 400 Evacuator, Jackson-Pratt Closed Wound Suction Drainage System, and Snyder Hemovac 400. Each drainage system was connected to a pneumatic pressure transducer, and pressure measurements were made. Measurements were made with the drain reservoirs at varying degrees of fullness. Measurements were also made while "stripping" the drains. In all three systems, maximal negative pressures (-71 to -175 mm Hg) were generated with the reservoirs empty of fluid. Pressure generation by all drains decreased as the volume of fluid in the reservoir increased. In all cases, drain "stripping" was associated with a transient elevation in drain pressure (p<0.05). In two out of three drains, stripping led to a significant residual increase in static drain pressure. Closed suction drains are capable of generating high pressures that may contribute to some complications associated with their use. Closed suction drainage systems differ with regard to their generation of negative pressure.