PIP: International cross-sectional data for 1975 were used to examine the relationship between fertility and socioeconomic development in 116 developing countries. The choice of countries was based primarily on the availability of data on some major development indicators. These 116 countries account for about 98% of world population, with the exclusion of mainland China. The study included 34 economically more developed countries and 82 economically less developed countries. Countries more developed included 27 developed market countries, 6 centrally planned economies of Eastern Europe, and the USSR. The less developed countries included in this study have market economies with the exception of Viet Nam, which has a centrally planned economy. The 18 development indicators were classified into 3 categories: 8 demographic indicators; 8 social indicators; and 2 economic indicators. This study tests 1 aspect of the relationship between fertility decline and socioeconomic development, i.e., the threshold hypothesis. The central point of this hypothesis is that fertility levels resist forces tending towards a decline until a certain level of development is achieved. Beyond this point, fertility eventually will fall to a relatively low level. The evidence suggests that changes in levels of development variables may have little impact on the level of fertility in countries of the high fertility group, but fertility levels are related to development variables in the medium and low fertility group. The results conform with the threshold hypothesis. The regression results generally are consistent with the conclusion of past studies and support the recommendation that development policy should consider the effects of development variables such as education and health on fertility change rather than continuing to treat the fertility change as an exogenous variable in the development process. The study results are consistent with the hypothesis that specific socioeconomic development variables will not affect fertility levels until certain threshold levels of those variables are reached.