Pentazocine (Talwin) originally was believed to be a safe, nonaddictive analgesic, but further experience has shown that severe mental and emotional disturbance, as well as addiction, may occur. This survey documents the experience in the Texas Medical Center and elsewhere. The accumulated data show the following: (1) Depressive states are reported most frequently, while toxic psychoses, hallucinogenic reactions with panic, and paranoid states on withdrawal of the drug are less frequent. (2) Of the 197 cases of addiction reported to date, only six were related to oral use of the drug. The abstinence syndrome is mild, consisting usually of restlessness, nausea, cramps, and insomnia. (3) Convulsions have been reported on four occasions. Euphoria and psychotomimetic effects may relate to rapid release of noradrenaline and dopamine. Oral use of the drug is advised to avoid euphoriant effects and addiction, and physicians should alert patients to report unusual visual phenomena. Tranquilizers are of value in cases of severe reactions.