A. Kalinskie1 and T. D. Chapman et al.2 have presented two interesting and divergent comparisons of the air and high purity oxygen activated sludge processes. Kalinskie has analyzed the claims of the Union Carbide Corp. (UCC) with respect to the properties of the oxygen activated sludge (UNOX) process and the comparison of air activated and oxygen activated sludge. Chapman, et al. have prepared UCC’s response to Kalinskie’s analysis and questioned the basis of his discussion.