Since Friday, Dr. Crouch's department has received 600 to 700 calls about suspicious materials, and he said, "Obviously, we can't test them all."

Still, the agency advised residents to wear gloves and wet any suspicious material before throwing it away, so that fibers do not become airborne.

At least five companies had scares and evacuations as a result of suspicious material arriving in their offices and mailrooms.

Dealers must be prepared to report unprovenanced or suspicious material to the police.

There are several tests used to detect ricin, including tests for environmental samples of suspicious materials, and for clinical specimens from human body fluids.

But investigators said yesterday that they found no trace of any suspicious materials.

The envelopes contained also suspicious material, which alarmed Slovak military police and security services.

Via clerk Marc Bellevile later testified that a subsequent search of the premises had been made, but turned up no evidence of suspicious material.

To take necessary measures for untethered mines, explosives and suspicious material identified in the sea and on the coast and report them to the authorities concerned.

This assists officials at seaports and airports in their inspections, and allows for the tracking of suspicious materials.