The effects of an ice wrap, applied to a knee for 20 minutes, on blood flow and bone metabolism were measured using triple-phase technetium bone scans. Twenty-one subjects between 29 and 63 years of age were studied. A commercially available ice wrap was applied to one knee 20 minutes before scanning, while an identical wrap left at room temperature was applied to the opposite knee to act as a control. Scans of the knees were obtained at the completion of cooling, and the images were quantified by computer image analysis for each knee at each phase of the scan. Percentage of decrease in blood flow and subsequent bone uptake of technetium for the iced knee as compared with the opposite knee were calculated. All iced knees demonstrated decreased arterial and soft tissue blood flow as well as decreased bone uptake, which is a reflection of changes in both bone blood flow and metabolism. The average decrease was 38.4% +/- 4.97 in arterial blood flow, 25.8% +/- 2.04 in soft tissue blood flow, and 19.3% +/- 2.0 (standard error of the mean in each) in bone uptake. This "ice effect" was not related to age, sex, knee circumference, or skin temperature after cooling. By decreasing blood flow and cell metabolism, ice theoretically can limit hemorrhage and cell death in the setting of acute traumatic injury. This study thus provides a scientific rationale for the use of ice as tested for such injuries to a large joint, whether in the soft tissues or bones.