A study was performed on human subjects to assess the effectiveness of single-dose immunization with 20 CU (1 ml) of adsorbed tetanus toxoid followed by revaccination with 10 CU (0.5 ml) 1 year later. Out of 1187 students, only those were selected for observation whose blood serum did not contain tetanus antitoxin (titre less than 0.001 IU/ml); this group counted 283 students. After administering the 20 CU (1 ml) of toxoid the antitoxin titre was repeatedly checked on days 10--15 and persons whose titre had risen to over 0.01 IU/ml were excluded from observation. The remaining 109 persons were tested for the antitoxin level 1 year later and revaccinated with 10 CU of tetanus toxoid. After 10--15 days their postrevaccination titre was determined. The single-dose immunization with 20 CU of tetanus toxoid in human subjects not given tetanus antigen previously was accompanied by a gradul rise in the antitoxin titre up to the protective level and its maintenance for 1 year (observation time) until revaccination. Revaccination with 10 CU of toxoid provided in 10--15 days a multiple (100--197fold) increase of the antitoxin titre, many times exceeding the protective level. The usefulness of transition to the shortened immunization scheme for tetanus prophylaxis of the adult population is discussed.