A B757 PILOT REPORTS DECLARING AN EMER AND DIVERTING TO A NEARBY ARPT WHEN CREW DETECTED FUMES OF UNKNOWN ORIGIN.

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ENRTE APPROX 90 MI E OF ZZZ AT A CRUISE ALT OF FL360; WE DETECTED FUMES FROM AN UNKNOWN SOURCE. WE DECLARED AN EMER; REQUESTED THE EMER VEHICLES; ACCOMPLISHED THE SMOKE AND FUMES REMOVAL CHKLIST; AND DIVERTED TO ZZZ. THE APCH AND LNDG WERE UNEVENTFUL. AFTER LNDG I REQUESTED THAT THE FIRE/RESCUE PERSONNEL INSPECT THE ACFT. THEY INDICATED THAT THEY DID NOT OBSERVE ANYTHING OUT OF ORDER. FUMES WERE PRESENT BUT NOT GETTING WORSE. CONDITIONS DID NOT WARRANT AN EVAC. I ELECTED TO TAXI BACK TO THE GATE WITH AN EMER VEHICLE TO FOLLOW US. I WANTED THEM TO OBSERVE THE ACFT FROM THEIR VANTAGE AND TO ASSIST US WITH AN EVAC SHOULD OUR SITUATION WORSEN. APPROPRIATE FOLLOW-UP CHKLIST AND PA'S WERE ACCOMPLISHED. THE FLT ATTENDANTS INDICATED THAT THE LINING OF THEIR NOSES AND THROATS FELT IRRITATED. I REQUESTED THE EMT'S CHK THEM OUT. THE EMT'S INFORMED ME THAT THEY HAD NO LIFE THREATENING PROBS BUT IT MIGHT BEHOOVE THEM TO GO TO THE LCL HOSPITAL FOR A MORE THOROUGH CHK OUT. I CONCURRED AND HAD THEM TAKE THE FLT ATTENDANTS TO THE HOSPITAL. AFTER ARR AT GATE I CONTACTED THE DISPATCHER; DUTY PLT; MAINT; AND A REPRESENTATIVE FROM THE CHIEF PLT'S OFFICE VIA A CONFERENCE CALL TO EXPLAIN WHAT HAD HAPPENED. I WENT BACK TO THE ACFT TO MAKE A LOGBOOK WRITE-UP AND TOGETHER WITH THE HELP OF THE AGENT AND FO TOOK OFF THE PAX'S PERSONAL BELONGINGS.