Many researchers have contributed to the field of international purchasing; but there are no consistent findings to illustrate particular connections within the field. This particular research studies the ways that two Iranian producers of polymer piping systems handle international purchasing in current complex Iranian economic circumstances. By going beyond macroeconomic theories of international trade and using three-factor model of international industrial purchasing this particular study aims to reveal how international industrial purchasing is handled by Iranian producers of polymer piping systems under current Iranian economic and politic circumstances. A case study approach employing face-to-face semi-structured interview method is designed. A set of interview questionnaires was designed to gather empirical qualitative and quantitative data. A narrative analysis was then conducted to lead the discussions and to draw conclusions. The results of the study show that international purchasing in both firms is influenced by internal factors including attitudes and competence as well as external factors including market conditions and regulations. The levels to which the first three mentioned factors influence international purchasing varies between the studied firms; but regulations have similar effects on the ways the studied firms handle international purchasing. Also, the modified three-factor model is perfectly applicable to the studied cases under current circumstances of Iranian economy.