In this investigation, the effect of alloying on catalysis, especially with respect to oxygen and the ORR, was examined. A series of alloys allowed four major aspects of alloying to be investigated: (i) effect of decreasing lattice parameter with increasing Cr content in the Pt terminal solid solution, (ii) effect of an order/disorder transition, (iii) difference between intermetallic and solid solution structures, and (iv) effect of dendritic segregation. Results indicated that contrary to the findings of previous investigators, decreased lattice spacing did not correlate with an increase in ORR activity. Atomic ordering in low Cr content specimens, however, was found to generally increase catalysis. Results also indicated that disordered structures interact more strongly with impurities than the ordered structures. ORR Tafel slopes, however, were unaffected by atomic ordering although additional chromium, up to at least 35 atom percent (a/o), caused a decrease in Tafel slope apparently due to oxide reduction effects. At higher Cr concentrations, catalysis decreased due to the passive nature of chromium oxide. The change in crystal structure which occurs for the 80 a/o Cr sample and the dendritic structure, had little effect on most of the electrochemical parameters studied relative simply to the additional Cr content. The results of this work also indicated that, in general, no alloy in the system is more catalytic than pure Pt. This result is in contrast to gas diffusion cell studies which have shown significant increases in catalysis due to alloying.