Adolescents today have to live with incoherence for longer periods than before, and that makes ambiguity tolerance a socially significant personality dimension. Studies of the development of ambiguity tolerance in adolescents are reported. The pilot study, "Adaptation of MAT-50 for Use with Bulgarian Population," involves translation and adaptation of the test for use in Bulgaria. Analysis of the pilot data is discussed. Study 1, "Cross Sectional Analysis of the Development of Ambiguity Tolerance in the Age Interval 15-25 Years," provides insight into the psychometric characteristics of the MAT-50/BG-2 and reports on differences in ambiguity tolerance related to subjects' sex, age, and education. Study 2, "How Ambiguity Tolerant Adolescents Compare with Those Who Are Intolerant of Ambiguity on Different Cognitive and Personality Characteristics," reports on selection of the group of high and low ambiguity tolerant adolescents. Study 3, "How the Attitudes of Teachers and Parents Influence the Development of Ambiguity Tolerance in Adolescents," addresses the differences in ambiguity tolerance related to subjects' sex, age and settlement; differences in AT-AInT values and parents' self-reported AT-AInT encouragement; and relationships between students' ambiguity tolerance and parents' self-reported AInT encouragement. Results and conclusions are discussed with emphasis on the educational implications of ambiguity tolerance. The Parents-Teacher Ambiguity Tolerance Survey is appended. (Contains 23 references and numerous tables and figures.) (EMK)