We present the results of ROSAT PSPC and HRI observations of two distant clusters, MS0735+74 and MS0451−03, selected from a sample of serendipitous X‐ray sources. MS0735+74 atz=0216 is a cooling flow candidate because it has extended H&agr; emission in the central brightest galaxy. MS) 451−03, atz=0.55, is the most luminous cluster in the Extended Medium Sensitivity Survey withLx≳1045ergs−1. We have been able to place significant limits onTx, core radii and the &bgr; parameter, and cooling flow contributions. Our preliminary results show that ‘‘cooling flows’’ can be identified by their extended H&agr; emission. Distant clusters probably do not have more intrinsic absorption than nearby clusters. More tentatively, luminous clusters at high redshift may be cooler and may have somewhat lowerMgas/Mtotal(at 1 Mpc scales) than the clusters of comparable luminosity at low redshift. ©1994 American Institute of Physics