Research assumptions and procedures of two studies of interlanguage (IL) phonology are examined and criticized. In both studies, syllable structure is used as a primary variable, but opposing claims are made about "open" and "closed" IL syllable structure preference. It is argues that: (1) neither IL study considers sufficiently the phonetic structure of the native language and target language; and (2) that syllable structure analyses based on broad categories such as "open" and "closed" are inadequately equipped for insightful IL investigation. It is recommended that in future research, less emphasis be placed on verification of second language learning processes and constraints and more emphasis be placed on reexamining, identifying, and describing the native, target, and interlanguage structures that previous researchers have assumed to be implicated in those processes and constraints. A brief bibliography is included. (Author/MSE)