A SERIES OF TESTS WERE CARRIED OUT TO ASSESS THE EFFECTIVENESS OF EXISTING VAPOR SENSING TECHNOLOGY AS AN AID IN DETECTING CONCEALED BOMBS ON COMMERCIAL AIRCRAFT. IN THESE TESTS, VARIOUS TYPES OF SIMULATED BOMBS WERE PLACED IN THE CABIN COMPARTMENTS OF DC-8'S AND OTHER PLANES. TRAINED TEAMS WERE THEN SENT ABOARD TO LOCATE THE DEVICES. A TOTAL OF SEVEN COMMERCIALLY AVAILABLE ELECTRONIC SNIFFERS WERE EMPLOYED IN BOTH A PRIMARY SEARCH ROLE AS WELL AS IN A BACKUP ROLE TO ESTABLISHED HAND SEARCH PROCEDURES. FOR COMPARISON, THREE POLICE DOG/HANDLER TEAMS WERE ALSO EMPLOYED IN THE SEARCHES. DURING THE TEST PERIOD IN THE FALL OF 1976, OVER 50 INDIVIDUAL SEARCHES WERE CARRIED OUT IN MONTREAL, CANADA, EACH SEARCH INVOLVING AN AVERAGE OF 3 HIDES. HIDES WERE COMPRISED OF MILITARY AND COMMERCIAL EXPLOSIVES IN ADDITION TO BLANK SAMPLES. SEARCHES WERE CONDUCTED ON HANGAR-BASED AIRCRAFT AT ROOM TEMPERATURE AND ON AIRCRAFT PARKED OUTSIDE IN NEAR-FREEZING CONDITIONS. FURTHER SEARCH TRIALS WERE SUBSEQUENTLY CARRIED OUT IN OTTAWA. THE AVERAGE FIND RATE WAS 72 PERCENT. THERE WERE NO SIGNIFICANT DISCREPANCIES IN THE FIND RATES OF THE VARIOUS SEARCH TEAMS. THE AVERAGE SEARCH TIME WAS 29 MINUTES. OF THE METHODS EVALUATED, HAND SEARCHES WERE THE MOST RELIABLE. TRAINED DOGS HAD A SLIGHTLY LOWER FIND RATE THAN HAND SEARCHERS, WHILE THE ELECTRONIC DETECTORS PROVED TO BE OF ONLY MARGINAL VALUE AS A PRIMARY SEARCH TOOL. HOWEVER, AS A BACKUP TOOL FOR HAND SEARCHES, A SMALL BUT SIGNIFICANT IMPROVEMENT IN THE FIND RATE WAS RECORDED. THEY WERE ALSO USEFUL IN ABOUT HALF THE CASES FOR CONFIRMING THE PRESENCE OF EXPLOSIVE MATERIALS CONTAINED WITHIN A SUSPECT FIND. TABULAR AND GRAPHIC DATA ARE PROVIDED, ALONG WITH REFERENCES. (KBL)