IT IS STRESSED THAT ANALYTICAL DATA RESULTING FROM TOXICOLOGIC EXAMINATION ARE GENERALLY INSUFFICIENT TO ATTRIBUTE CAUSE OF DEATH TO ANY ONE SUBSTANCE. RESULTS MUST BE INTERPRETED WITH CONSIDERATION GIVEN TO INVESTIGATIONS AT THE SCENE, ACTIVITIES OF THE DECEDENT IMMEDIATELY PRIOR TO DEATH, FIRST AID OR TREATMENT EFFORTS PROVIDED BY LAYPERSONS OR BY MEDICAL PERSONNEL, AND LONG-TERM DRUG USE HISTORY. INDIVIDUALS MAY BE MADE MORE SUSCEPTIBLE TO SOME SUBSTANCES BY PREEXISTING PATHOLOGY OR LESS SUSCEPTIBLE BY TOLERANCE. DIFFERENCES IN SUSCEPTIBILITY TO TOXIC SUBSTANCES ARE DETERMINED IN PART BY GENETIC FACTORS. A DISCUSSION OF THE PHARMACODYNAMICS OF HOST-SUBSTANCE RELATIONSHIPS INCLUDES CONSIDERATION OF CARBON MONOXIDE AND BARBITUATES. A METHOD OF DETERMINING TOLERANCE TO SEDATIVE DRUGS IS DESCRIBED AND GRAPHICALLY ILLUSTRATED. FACTORS TO CONSIDER IN INTERPRETING TOXICOLOGIC FINDINGS ARE LISTED.