The major objective of this study was to assess the relationship of various components of the Beltsville Poultry Semen Extender (BPSE) to the maintenance of the fertilizing capacity of chicken semen stored at 5 degrees C. A secondary objective was to rest the effectiveness of certain chemical additives on maintining the fertilizing capacity of stored semen. The data indicate that the components of the BPSE which contribute most to the preservation of semen were sodium glutamate and potassium phosphate. Also the high level of potassium in the BPSE was critical to the survival of spermatozoa during low temperature storage. Although the fructose component of the BPSE was not a significant factor during storage, attempts to substitute fructose with other carbohydrates resulted in a reduction in fertility. The addition of gentamicin sulfate (100 to 200 microgram/ml.), or pasteurized milk (10% v./v.) to the BPSE did not significantly alter the fertilizing capacity of semen stored for 24 hr., whereas similar levels of whole egg, egg yolk, egg albumen or seminal plasma had a depressive effect. The data in this study clearly indicate that components of and additions to the BPSE were responsible for the maintenance of only about 50 to 60% of the fertilizing capacity of chicken semen stored for 24 hr. at 5 degrees C.