The growth of height and weight of 275 Japanese girls was followed longitudinally over a period of three years, which included the time of menarche. The association between height and weight at menarche was examined, using path analysis to describe the relationship. Two hypotheses (I and II) were evaluated: Hypothesis I. Menarche in an individual girl is triggered by attainment of a particular weight. Hypothesis II. Menarche in an individual girl is triggered after attainment of a particular threshold body size or weight. As the result of this analysis, no particular weight and/or height was observed which discriminates between girls who have attained menarche and those who have not attained menarche. Although the results did not disprove the importance of weight as a factor which influences the onset of menarche, it did not support the existence of a particular critical weight or threshold body size or weight. Instead, a more random pattern of growth before menarche was evident, i.e. there was no correlation between weight at one year before menarche and increment in weight during the year before menarche. To describe the observed relationship, an alternative hypothesis (hypothesis III) concerning the existence of a threshold phase between two years and one year before menarche is suggested. According to this hypothesis, menarche in an individual girl is triggered by attainment of a threshold phase of growth between two years and one year before menarche, although this phase is not defined by a particular invariant weight for each girl in a given population. There is a central tendency of weight in this sample of Japanese girls which lies between 31 and 36 kg of weight. After completing this phase, further weight increment before menarche in each girl occurs independent of the weight already attained during the threshold phase. At present, the biological meaning of the suggested threshold phase is not clear. In further studies, the growth curve of each girl between two years and one year before menarche must be followed carefully. / text