Recent progress of forensic toxicology of morphine and heroin, and of the boundary area was reviewed. Topics included in this review were 1) opioid peptides, 2) opioid receptors, 3) endogenous morphine, 4) metabolism of morphine : glucuronidation, sulfate conjugation, N-demethylation and dehydrogenation, 5) pharmacological activity of morphine conjugates, 6) metabolism of heroin, 7) analytical methods of morphine and heroin for forensic toxicological purpose.