Airborne compounds from two groups of plasticizers used in air conditioner filters and caulks as well as flexible polyvinyl chloride and related plastics have been identified as major sources of low level laboratory contamination that can cause serious interferences in pollutant analyses especially at the low levels requiring GCEC for quantitation. Two compounds from the phthalic acid ester group (PAE'S) OF PLASTICIZERS THAT ARE ENVIRONMENTAL POLLUTANTS AS WELL WERE FOUND INCORPORATED ON AIR CONDITIONER FILTERS LEADING TO CONTAMINATION OF CLEAN AND OIL FILMED DISHES FROM AIR FALLOUT. Solvents, inorganic reagents and hand-to-glass transfer were found to contribute to sample contamination by PAE's. Several PAE's are easily detectable at 0.1 ng levels under some conditions on GCEC and have retention times on several columns of differing polarities that can interfere with analyses of chlorinated pollutants especially p,p'-DDT. Aroclor 1254, a member of the polychlorinated biphenyl group (PCB's) of plasticizers, was found in a caulk around a laboratory window. On oil filmed, but not clean dishes, the compounds collected from air fallout produced chromatograms on GCEC with a close correspondence to Aroclor 1242.