They also found that the silicone can leak out of intact implants, increasing fears that the devices put women's long-term health at risk.
Campaigners seeking compensation for women who believe breast implants have made them sick say the report strengthens their position.
The women have complained of illnesses such as lupus or rheumatoid arthritis, which affect the connective tissue that holds the body together.
The study was published in Environmental Health Perspectives, a journal of the US National Institute of Environmental Health Sciences.
Injections
The study was carried out by Dr Michael Lieberman and colleagues at the Baylor College of Medicine in Houston, Texas.
They injected silicone into mice. Those given the highest doses died within three to five days.
The researchers said: "These mice developed inflammatory lesions of the lung and liver as well as liver cell necrosis."
Liver cell necrosis is where the cells die, and can lead to death.
The findings are significant because laboratory experiments have shown that the silicone can escape even intact implants, the researchers said.
"And in mouse experiments cyclosiloxanes (silicone) have been shown to be widely distributed in many organs after a single . . . injection and to persist for at least a year," they added.
Exposure
The Command Trust Network represents women with implants.
It said: "These findings indicate that low-dose exposure to these silicones over time may lead to chronic inflammation, chronic lung and liver disease and abnormal tissue growth.
"Because these silicones leak from even intact implants, there is a high potential of such exposure in implanted women."
Last December a panel of specialists said they had found no evidence that breast implants could make people sick.
The panel was appointed by a US federal judge.
It said tests that did show a toxic effect on the immune system were "few in number and questionable in significance".
Another panel of experts, appointed by the Institute of Medicine at the request of the US National Institutes of Health, started looking into the evidence last year.
Legal cases from implanted women complaining of ill health are pending against manufacturers Bristol-Myers Squibb, Baxter Healthcare and 3M.
Last July Dow Corning reached a $3.2bn agreement to settle cases by more than 400,000 women.
The company maintained that the implants do not cause health problems.
Background Briefings
Medical notes
Silicone implants safe says US inquiry
(02 Dec 98 | Health)
Breasts implants 'safe'
(06 Feb 98 | Sci/Tech)
Settlement reached in breast implant case
(09 Jul 98 | Americas)
Breast implant leak risk 'far higher than suspected'
(19 Dec 97 | Sci/Tech)
The Breast Implant Controversy: Documents and Pointers
Breast Implant Activists
3M Pharmaceuticals
Dow Corning
Baxter Healthcare
Anti-implant support page
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