A bstract-A nonparametric time series test is applied to the buyers' and sellers' (BLS) prices collected by George Stigler and James Kindahl. Although BLS pnrces are more ngid, the two senes of pnrces are sufficiently similar in behavior dunrng two business cycles so that one can reject the null that each is generated by different stochastic processes. Moreover, each series reacts similarly in favor of the administered price hypothesis: in recessions and in the initial year of recovery, concentrated pnrces are more rigid and perversely flexible than unconcentrated pnrces, which are characterized by random movements and changes in the direction of real demand.