This paper further develops the stock return method proposed by Cho and McKelvey (1996). It is claimed that the method may detect industry substructure in an objective and effective way. Although they are statistically significantly different while avoiding any artifactual statistical results (Barney and Hoskisson, 1990; Peteraf and Shanley, 1997), the groups found in Cho and McKelvey (1996) fail to show clear face validity. Furthermore, the one-year sample window used in their study may be too short of a time to capture a sufficient number of outside disturbances that are the basis for grouping. In this paper, the sample period windows are extended from the previous one-year window to 6 different windows, namely 1-year, 2-year, 3-year, 5-year, 7-year and 9-year window spans. To test its stability in different time periods, clustering results of year 2000-04 are compared to those of year 1988-96. By formally applying different sample windows and time periods, the limitations of small window and unknown stability (Cho and McKelvey, 1996) are supposed to be dismantled. Furthermore, this paper examines whether daily returns or weekly returns are better to use in the stock return method. Among the largest firms in their market capitalization, 30 sample firms listed in New York Stock Exchange or NASDAQ (NYDAQ) are carefully chosen from the steel, banking, and pharmaceutical industries. We find that the stock return method produces stable group classifications consistently across different sample windows and time periods. In our particular sample, the groups found show clear face validity, say its correct industry membership. As the time span increases from 1 year to 9 years, the group structures become clearer and tighter. The grouping structure found in the 1988-96 time period has been consistently maintained in the 2000-04 time period. Daily returns produce the same grouping results with those from weekly returns, but they are better because they can detect groups sooner or with smaller time windows. Several conclusions are drawn from the study. First, the stock return method can effectively identify industry substructure as maintained in Cho and McKelvey (1996). The findings confirm that industry substructure can be reliably and validly separated, and that substructure stability has been longitudinally maintained across different sampling windows and time periods. Second, the identified group structure is not artifactual. The historically consistent results from our method using 'hard' market-equilibrium data render a high level of validity on our finding. Third, the findings are objective because the sample data used are 'hard' data, and the stock return method has no subjective decisions buried within it (including clustering methods).