The text of a letter to Operations Research commenting on an inventory model for items that may be either repaired or discarded. Instead of the approximation used by the authors, an exact expression is derived for the long-run expected shortages per unit time if reorder time is less than or equal to repair time (and another for the less usual case in which lead time is greater). The exact equation requires about the same computing time as the approximation. Numerical comparison of six cases showed that the approximation, when compared with the exact expression, overestimated the backorders by factors ranging from 2.5 to 5. 12 pp. Refs.