The Proficiency Analytical Testing Program (PAT) was described in this pamphlet. PAT provided reference samples to industrial hygiene laboratories to determine the proficiency of the various laboratories practicing in the industrial hygiene field and also to improve analytical performance. Bimonthly mailings were made of sample kits containing up to 15 filters and ten charcoal tubes. Each laboratory was required to test and submit results for all reference samples which were similar to the work load they normally handle. The analytical methods used were those normally used for such materials. The Chemical Reference Laboratory, under the PAT Program, also provided reference samples for short term special studies. The American Industrial Hygiene Association (AIHA) Laboratory Accreditation Program was described. Participation in the PAT program was restricted to government and university laboratories, private laboratories providing analytical services under a government contract, and private laboratories participating in the AIHA. The reference materials available from the National Bureau of Standards were listed. NIOSH training courses were listed along with several publications useful for laboratory and field reference.