Abstract “AIR sac disease” (Gross, 1961a) or complicated chronic respiratory disease (Fabricant and Levine, 1962a, b) in broilers causes growth depression and dressing plant condemnations. During 1960, over 15 million broilers were condemned because of this disease (U.S.D.A. Report, 1961). In an effort to establish the etiologic agent(s), extensive research has been completed (Gross, 1961a; Fabricant and Levine, 1962b; Dunlop et al., 1961; and Adler et al., 1957). Despite this, the exact cause(s) of complicated CRD seen in the field is an enigma. More work is needed to elucidate the role of Mycoplasma gallisepticum, pathogenic strains of Escherichia coli and the viruses of Newcastle disease and infectious bronchitis. Gross (1961a), Fabricant and Levine (1962b), Adler et al. (1957), and others, have made significant contributions. Epizootiologists may utilize these and future findings to eradicate this disease. If a feed additive in the presence of complicated CRD in broilers could improve production efficiency,…