The influences of hypothyroidism on behavioral measures of the taste function in male and female Long-Evans rats were determined. Experimental rats' preferences for and ability to detect NaCl, HCl, sucrose, and quinine sulfate were examined before, during, and after 9 weeks of maintenance on 0.1% propylthiouracil (PTU), an agent that produces marked hypothyroidism, with similar determinations made for control animals. Despite significant decreases in PTU-treated rats' serum triiodothyronine (T3) and thyroxin (T4), there were no changes in sensitivity or responsivity to the target tastants. However, altered preferences for NaCl, HCl, and quinine sulfate were observed for PTU-treated rats; elevated consumption of HCl and quinine sulfate was present at the end of the study when serum T3 and T4 had returned to near-baseline levels. The data confirm observations that PTU-induced hypothyroidism alters rats' taste preference behavior.