Abstract: Introduction In a recent paper [1] Misra had introduced a metho d of verification of loop programs based upon a given loo p specification. This method employs the ideas of Mills [3 ] and is close to the subgoal induction advanced by Morris an d Wegbreit [2]. In this work we apply a variation of the metho d to program debugging showing how a loop and its specificatio n can be checked for consistency and correctness and possibl y corrected. The method requires an initialization be remove d from the loop construct and its specification be defined so a s to explicitly show the dependence of the final values on th e initial values of the variables of the loop treated as a separat e entity. The presentation is informal, being illustrated wit h a simple example. In what follows a*B stands for the whil e a do B construct, where B : D-> D is the loop body, and D is the domain of a*B. Greek letters stand for vectors o f variables of D. F stands for the function computed by a*B .