In 1957 Otto SCHAUMANN, one of the pionieers in pharmacological research on morphine and the first to prepare synthetic opiates, presented a monograph entitled "Morphin und morphiniihnliche Verbindungen" as Volume 12 of the Handbook of Experimental Pharmacology. Now, 35 years later, we are publishing in the same series a new comprehensive volume covering the present status of opioid research. Since that time the topic has expanded enormously. The identification of opioid receptors and the detection of their endogenous ligands were landmarks which opened a new era in opioid research and fertilized the entire field of neurobiology. The rapid development of this field is illustrated in the figure, which represents the number of papers published on opioid research since 1970 (searches performed on the MEDLINE data base). 3000