In this work the role of energy substrates in the maintenance of boar-sperm survival during storage at 15-17°C was tested. For this purpose, boar spermatozoa were stored at 15-17°C in several defined media with separate combinations of a monosaccharide, glucose and a non-monosaccharide, either citrate or lactate, energy substrates. Our results indicate that the medium containing the highest concentration of glucose together with low lactate levels was the most suitable to maintain sperm quality for 168 h at 15-17°C. This was confirmed after observation of the results of the percentages of viability and altered acrosomes, the osmotic resistance test, the hyperosmotic resistance test and the rhythm of l-lactate production. The survival ability of boar sperm was greater in this experimental medium than in the standard Beltsville Thawing Solution extender, which contains only glucose as an energy substrate, although at a concentration far higher than that of all the tested experimental media. Our results indicate that the exact composition, more than the pure quantity of energy substrates, is a very important modulatory factor which affects survival ability of boar sperm in refrigeration. Thus, the exact combination of several energy substrates would have to be taken into account when optimizing the design of commercial extenders to store boar spermatozoa at 15-17°C. © 2005 Blackwell Verlag.