Scientists are taking the first steps toward creating alternative life forms — organisms that use a genetic code different from the one used by all other creatures on earth.
Scientists hope that such organisms can be used to study biochemical processes in new ways and to produce new medical or electronic materials that cannot now be made by living things.

The research goes well beyond current genetic engineering, which involves reshuffling the ordinary components of DNA or proteins into new combinations or moving DNA from one organism to another. Adding completely new elements to DNA and proteins is essentially rewriting the genetic code. It is likely to raise new ethical and safety issues.

Dr. David A. Tirrell, chairman of chemistry and chemical engineering at the California Institute of Technology, has gotten bacteria to make a protein with the nonstick properties of Teflon by having the microbes substitute an unnatural amino acid for one of the 20 natural ones. He said such a protein might one day be used to make artificial blood vessels.

Dr. Peter G. Schultz, director of the Genomics Institute of the Novartis Research Foundation, wants to subject bacteria with extra synthetic amino acids to stresses like heat or poison to see if they evolve and adapt faster than natural bacteria. “Will those forms of life with a bigger building-block set be superior to the ones who have 20?” he asked.