This article reports the findings of a longitudinal study in interlanguage phonologyexamining the production of two structures in a markedness relationship, biliteral and triliteralonsets, the latter being more marked than the former. This study specifically tests theInterlanguage Structure Conformity Hypothesis (ISCH) by measuring the acquisition of theonsets in the markedness relationship against a criterion measure of 80% correct production. Thesubjects were 10 native Spanish speakers enrolled in intermediate courses in a communitycollege. Data were gathered twice over a period of 10 months. Results of the study fail to provideany counterevidence to the ISCH.