A study was made of the responses of schoolchildren to tuberculin testing 2 months and 5 years after vaccination with one of 11 different BCG vaccines prepared by several laboratories from different strains. The fact that the allergenic response was almost unchanged after 5 years shows that a long-term follow-up adds nothing of any significance to the information obtained 2 months after vaccination. The study also showed that postvaccinal tuberculin testing is only of value in determining the level of the allergy in groups of persons. It yields little information on the level in individuals since several factors, including unavoidable experimental errors and unknown personal factors, greatly influence the reaction.