SUMMARY.Hynes&Coleman (1968) proposed a method for estimating benthic secondary production for use with populations in which cohorts cannot be distinguished and for use with unidentified benthos. Hamilton (1969) corrected and refined the method, emphasizing the concept of the average cohort. Zwick (1975) recently suggested the method should not be used since: (1) too many conditions need to be filled for use with unidentified material, and (2) it is strongly dependent on growth patterns. This paper shows that Zwick misinterpreted the concept of the average cohort, and his apparent invalidation of the method due to dependence on growth patterns is erroneous.