The antitoxin titer, at different time intervals from the administration of 250 I.U. of specific immunoglobulins, was determined by means of passive hemagglutination in the serum of 28 non-immune subjects, selected among the wounded hospitalized at a First Aid Station. The maximum titer of circulating antitoxin was reached in the majority of the cases, already after 6 hours. Twenty-four hours after the inoculation, 62.5% of the treated subjects showed antibodies with a titer equal to, or higher than, 0.01 I.U./ml. Nine of the subjects, who showed antibodies, were monitored for 30 days. The level of tetanus antitoxin was not appreciably modified within the first 10 days. Between 11 and 20 days the titer, even though reduced on the average, remained above the minimum protective level of 0.01 I.U./ml, while after 21-30 days, this titer dropped under this value in three out of 6 subjects.