This study examined the relationships between temperament and ecological context among Yucatec Mayan children based on the assumption that maternal ethnotheories act as mediators and are related to world view. Since the latter is related to ecological context, its transformation may result in variations in ethnotheories and, therefore, temperament characteristics. Using standard questionnaires and ethnographic data, we evaluated 178 children aged 4 to 36 months from two villages representing the most contrasting ecological contexts in Yucatan, Mexico. Mothers described temperament-like behaviours as "modos" (ways) and related them to their concepts of development and children's vulnerability, and to child-care and rearing practices. Age predicted threshold, approach, and intensity. Ecological context independently contributed to variations in approach, intensity, mood, and distractibility. Parental characteristics did not independently contribute but appeared to influence the relation between ecological context and mood, intensity, and distractibility. The findings suggest that temperament variations associated with ecological context may result from differences in maternal ethnotheories about rate of development and vulnerability of children and that knowledge of the national language and increased education without transformation of ecological context may have influenced ethnotheories on rate of development rather than on vulnerability. (Contains 4 tables and 4 footnotes.)