Several factors, including age, sex, race number, post position, and race class, were evaluated for relationships to prerace percentage body weight loss and performance in all Greyhounds racing during August 1983 in Oregon. The incidence of percentage body weight loss greater than or equal to 2.5% was low (5%). Race number had a direct effect on weight loss; the later the dogs raced, the more weight loss they experienced. Female dogs were 3 times more likely to lose greater than 2.4% of body weight than males. All dogs experiencing greater than 2.4% body weight loss were 2 times more likely to finish in the first 3 places when racing in the first 5 races overall. In addition, males losing greater than 2.4% of body weight performed better than females when racing together in the final 6 races. Males appeared to be better performers than females, as they were twice as likely to be in class A races. However, once in the race, males and females performed equally.