The purpose of this study was to investigate two hypotheses. The first stated that the structure of interests was similar across two cultures (United States and Mexico) using two levels (students and professionals) of males in a single occupation (engineering). Thus, holding occupation and gender constant, the cross-cultural similarity of the structure of interests was examined. Support was found for this hypothesis. The second hypothesis investigated three forms of Holland's calculus assumption concerning the specific structure of the six occupational themes. Holland's calculus assumption states that the distance between all adjacent occupational types (e.g., RI) is less than the distance between all alternate types (e.g., RA) which, in turn, is less than the distance between all opposite types (e.g., RS). A more stringent form assumes that the six themes form the vertices of an equilateral hexagon, while a weaker form merely asserts that the structure of the occupational themes is circular. The calculus assumption was supported, thereby also supporting the assumption of a circular structure. Evidence in support of an equilateral hexagonal structure was not found. © 1992.