The tranquillizers are classified into five main categories: (1) major tranquillizers (phenothiazines, Rauwolfia alkaloids): (2) Compounds of intermediate activity (tetrabenazine, chlorprothixene, prothipendyl and haloperidol): (3) minor tranquillizers (diphenylmethanes, frenquel, benactyzine, hydroxyzine, atarax); (4) tranquillosedatives (meprobamate, carisoprodol, chlordiazepoxide, chlormezancine and emylcamate); (5) hyponsedatives; psychosethatives (barbiturate and non-barbiturate sedatives and hypnotices). Clinical activity, pharmocological properties, indications and side-effects are described and tabulated. Dosage for commonly used tranquillizers is also given.