Radiolucent breast implants filled with triglyceride oil have recently entered limited clinical trials. To investigate the questions of oil bleed and the fate of triglycerides that might escape from ruptured breast implants, experiments reported here used peanut oil labeled with radioisotopes so that it could be traced in the urine, feces, and organs of two groups of rabbits. In one experiment, 18 rabbits were implanted with peanut oil-filled implants labeled with tritium to determine whether triglycerides diffuse across silicone elastomer shells. In another experiment, 19 rabbits were injected with 14C-labeled peanut oil to study what might happen to the oil if an implant ruptures. At the end of the follow-up period, we measured radioisotope levels in tissue samples taken from the periprosthetic capsule or injection site of each rabbit, as well as from major organs and the subcutaneous fat on the dorsum opposite the experimental site. One experiment revealed that triglycerides do bleed across the implant shells. Tritium levels were highest in the implant capsule, the omentum, the aorta, and the subcutaneous fat on the nonexperimental side. In the experiment simulating implant rupture, 14C levels were above the background radiation count at the injection site and in the same tissue sites as in the bleed experiment. Both in vivo radiolabeling studies indicate that triglycerides freed from implants by means of bleed or rupture would be absorbed, metabolized, and either excreted or redistributed to the body's normal fat storage sites if they are not needed for energy. In a third in vitro experiment, triglyceride oil specimens were inoculated with various microorganisms associated with wound infections: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, and diphtheroids. The data demonstrate that neutral triglycerides used as a breast implant filler do not support growth of common infection-producing bacteria and suggest that triglycerides may have bactericidal properties.