Xytronyx Inc. lost more than half its market value Friday afterit announced that it has received a letter from the Food andDrug Administration stating that the company's pre-marketapproval application for the PerioGard Periodontal TissueMonitor Kit is not approvable.

The company's stock (AMEX:XYX) plummeted $14.38 to close at$13.25.

The FDA letter cited several deficiencies that must be resolvedto make the PMA approvable, according to a statementreleased by the San Diego-based company. Xytronyx said theprocess of resubmission and regulatory consideration willrequire a substantial amount of time.

Company officials did not return calls for further comment.

The kit detects gum disease by measuring enzymes secreted byinfected gums.

The FDA has previously approved export of the kit to Denmark,Italy and Greece. That approval is unaffected. Colgate-Palmolive Co. is the exclusive worldwide distributor of the kit.

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