Adult Fischer-344 (F-344) rats fail to prefer NaCl solutions of any concentration to water and, in fact, avoid NaCl at solution concentrations which other strains of rats reliably prefer. In contrast, immature rats of a number of strains have been reported to express an elevated salt preference relative to adults. The present studies examine the development of the F-344 rat's salt aversion by testing salt preference in the preweaning (Day 10) and weanling (Days 20-24) F-344 rat. At Day 10, F-344 rats ingested significantly more 1% and 2% NaCl solutions than water during "towel testing" and their preference was comparable to that displayed by other strains at this age. By the time of normal weaning (Days 20-24) significant avoidance of NaCl solutions in the isotonic range was displayed by F-344 rats, and their preference was strikingly different from other rat strains. This was evident in a 24-hr 2-bottle preference test as well as a 25 min "towel test." Since NaCl preference of F-344 rats is comparable to other rat strains at Day 10 but dramatically different by Day 20, a change must occur during this time which reverses the hedonic value of NaCl stimulation. Identification of factors responsible for this reversal may provide insight into the causes both of the F-344 rat's dislike of salt and the immature rats elevated salt preference.