Because the consequences of a positive drug test can be severe, laboratories that conduct such tests must rigorously follow a carefully designed quality assurance (QA) program. Such a QA program should include the use of reference materials to ensure that the methods used to detect and quantify drugs are providing accurate results. The NIST supports accuracy in drug testing by providing Standard Reference Materials (SRM's) with certified concentrations of drugs of abuse in urine-based and hair-based reference materials. NIST, working in collaboration with the College of American Pathologists (CAP), has developed urine-based SRM's for marijuana metabolite, cocaine metabolite, morphine and codeine, and morphine glucuronide and CAP Reference Materials for amphetamines and phencyclidine. Certification measurements performed at NIST involve two independent methods for each analyte, one of which always uses gas chromatography/ mass spectrometry (GC/MS) with the other usually being an LC method with either MS or UV detection. Work has recently been completed on a seven-component drug in urine SRM. In addition, NIST conducts research on the analysis of hair for drugs of abuse. To assist laboratories that test hair for this purpose, NIST has developed two drug-in-hair reference materials. 4 tables and 7 references