The effects of exposure to xylene on performance of tests of numerical ability, reaction time, short-term memory and critical flicker fusion was studied in two separate laboratory studies. The exposed period was 70 minutes. Exposure to xylene did not cause any noticeable change in performance during the first laboratory series (xylene uptake 180 mg and 540 mg, respectively). In the second series, physical work induced an increase in the total uptake (1200 mg) with evidence of performance decrement. -- AATA