BACKGROUND The ability of a sterile connecting device to maintain sterility when being used to weld tubing of a blood component to be stored at room temperature, such as a platelet unit, has not been adequately documented, nor has it been determined when the tubing to be welded is filled with liquid. METHODS The sterility of sterile connecting device welds of polyvinylchloride tubing were challenged after intentional contamination of the exterior of the tubing with both gram-positive and gram-negative organisms (4 x 10(4) to 3 x 10(6) colony-forming units/mL). Welding (n = 244) was performed with the contaminated area either being wet or having been allowed to dry. At the time of the welding, the tubing segments were either empty or filled with liquid (either aliquots of white cell-reduced apheresis platelets or bacteriologic growth medium). After the welding, the liquid was passed across the weld and held in the attached transfer pack for 5 to 7 days at room temperature. RESULTS Two welds were found to be incomplete and leaky, and both of the units involved had positive cultures. One transfer pack had inadvertently been contaminated at the time of its initial, postweld culture by a bacterium other than the one used in the experiment. Aside from these three nonevaluable units, all of the welds were sterile when cultured after the packs were held for 5 to 7 days. CONCLUSIONS This study documents the ability of the sterile connecting device to maintain a closed system in the welding of blood component units to be maintained at room temperature. All welds should be closely inspected at the time of completion to detect leaks that may lead to contamination.