SAN FRANCISCO -- Scientists from two rival companies announced Thursday they had succeeded in placing vital bits of man's 30,000 genes on a chip the size of a dime, bringing so-called personalized medicine one step closer to reality.

Affymetrix Inc. and Agilent Technologies produced so-called gene chips -- small pieces of glass infused with genetic material. Until Thursday, Affymetrix and Agilent needed two chips to hold the same genetic material.

Chips with parts of the genome have become indispensable in biology labs around the world. Now, Affymetrix, the industry leader, said researchers can buy the entire genome for between $300 and $500 each -- roughly half the old price.

"It's a significant milestone," said Affymetrix chief executive Stephen Fodor.

Employing semiconductor manufacturing technology, workers "print" genes one molecule at a time onto the glass until they stand up like microscopic skyscrapers, each about 25 molecules high.

Researchers then drop onto the chips specially tagged RNA. The portion of a chip on which genes interact with the RNA becomes fluorescent, highlighting bad genes that may need a closer look.

The twin announcements Thursday came on the heels of similar breakthroughs by Applied Biosystems of Foster City and Madison, Wis.-based NimbleGen Systems, both of which said in July they had created a genome on a chip. In addition, a research team from two German science institute made a similar announcement last year.

Because Affymetrix owns 80 percent of the commercial market, however, its announcement was greeted as an industry turning point.

Even the chips touted Thursday, however, don't contain whole genes. Instead, they contain vital pieces of each gene. But more genetic detail is expected to be added to the chips in coming years, making them more powerful and versatile.

Today, researchers mostly use the chips for basic genetic research.

Scientists believe many diseases are caused by genes "turning on" when they shouldn't. Knowing this, researchers can design drugs to attack suspect genes.

Until gene chips came into vogue about five years ago, genetic scientists slogged slowly through their research, often investigating one gene at a time. Now they can analyze thousands of genes simultaneously, more quickly identifying disease causes.

Researchers even envision a day when pediatricians and other physicians can be armed with the chips, technically called microarrays. The hope is that a drop of a newborn's blood can quickly be converted into a genome on a chip. From there, a doctor could determine the baby's predilection to disease and other genetic traits.