Preliminary results from a 90-day inhalation study in rats indicated that sedative effects occurred during exposure. In this study, 18 rats per sex per group for the control and high concentrations and 12 rats per sex per group for the intermediate doses were exposed to 0, 500, 1500, or 3000 ppm THF for 6 hours/day, 5 days/week, for 13 weeks (90 days). The animals' response to an alerting stimulus (a standardized noise caused by striking the metal test chamber with a metal object) administered during each exposure period was evaluated and recorded. Since all of the animals were not visible through the chamber window during this evaluation, no attempt was made to quantify the number of animals in each chamber that responded- rather, the judgment about the teaction of the group as a whole was recorded. Functional observational battery and motor activity evaluations were conducted prior to initiation of exposure, and after 4, 8, and 13 weeks of exposure. A subset of the control and 3000 ppm concentration groups was allowed to recover for 4 weeks.