We are of the opinion that the use of streptomycin injections is definitely benefitial in controlling infectious coryza of chickens. Seventy of the seventy-eight infected, untreated control birds did not recover from coryza; 10 of these control birds died from coryza infection during the observation periods; 8 birds in the control group made an apparently spontaneous recovery for which we have no valid explanation. Whereas any treatment with streptomycin injection proved better than no treatment, the lowest dose used in these trials, i.e., 0.05 gm. subcutaneously per bird, did not seem to be effective in a large proportion of the birds treated under our experimental conditions. A single 0.10-gm. dose of streptomycin per bird proved to be more effective in curing and checking coryza than the 0.05-gm. dose. The effectiveness of the 0.10-gm. dose used subcutaneously, varied from 12.5 to 37.5 percent when the coryza-infected birds were kept in batteries in the presence of infected, untreated controls. When the single 0.10-gm. dose was injected intramuscularly, its effectiveness increased to 92.9 percent, even in the presence of infected, untreated controls in the same hen house. The effectiveness of the 0.15-gm. intramuscular dose was 75 percent. The highest effectiveness, 96.4 percent, was noted when a single intramuscular 0.20-gm. dose was used per bird. The 0.25-gm. dose had an effectiveness of 83.3 percent when injected subcutaneously, and 85.7 percent intramuscularly. We believe that the cost of the higher streptomycin dosage-levels (0.20 and 0.25 gm.) may preclude their extensive use in commercial poultry flocks, especially so when their respective effectiveness is not substantially (significantly) greater than that of lower, cheaper streptomycin doses. The use of a single, intramuscular dose of 0.10 gm. of streptomycin per bird affected seems to be an economical, efficient, and reliable means for the control of infectious coryza or "moquillo" of poultry.Las inyecciones de estreptomicina son eficaces para controlar el "moquillo" de las aves. Las aves que se trataron con la estreptomicina mejoraron o curaron del "moquillo" en una proporción mayor que las que se dejaron sin administrarle la droga. Sin embargo, es bueno apuntar, que la concentración de 0.05 gramo de estreptomicina, la más baja en los ensayos, aplicada subcutáneamente a cada ave, dejó de surtir los efectos de curación esperados. Cuando se inyectó la estreptomicina en concentraciones de 0.10, 0.15, 0.20, y 0.25 gramo por ave, la eficacia de la droga en contra de la enfermedad fué de 92.9, 75.0, 96.4 y 85.7 porciento, respectivamente. Las inyecciones intramusculares fueron más eficaces que las subcutáneas. De acuerdo con los resultados, el aplicar una inyección intramuscular de 0.10 gramo de estreptomicina por ave enferma, es un método económico y casi seguro para controlar el "moquillo" aviar.