In many hospitals, waste materials and used linens from the rooms of patients in isolation or the clinical laboratories are routinely double-bagged to reduce contamination of the external surface of the bag that could be transmitted to hospital personnel subsequently handling them. No studies have prospectively examined the value, if any, of double-bagging. We randomly assigned waste and linens from the rooms of 42 patients in contact isolation to be transported in single bags or double bags. Shortly after a single (or double) bag had been set outside the patient's room, the surface was cultured quantitatively in two locations near the knot; over 2 months, 209 bags were cultured. Surface contamination by Staphylococcus aureus (3% to 5%), enteric gram-negative bacilli (6% to 7%), or either (9% to 12%) was infrequent and comparable in both groups; moreover, quantitative levels of contamination in the two groups were almost identical (mean, 27 and 29 colony forming units [cfu] per bag). These data suggest that there is no advantage, as regards asepsis, to double-bagging potentially contaminated items from isolation rooms or clinical laboratories as compared with using a single bag. The use of a single-bag system with a heavyduty bag, as compared with double-bagging, saved our hospital $9,400 in 1985.