The effect of the solvent white spirit on psychological functions, such as perceptual speed, reaction time, short-term memory, numerical ability, and manual dexterity, was studied in two separate series of experiments employing 14 and 8 healthy male students, respectively. Each subject was tested repeatedly in each series in exposure to 625, 1,250, 1,875 and 2,500 mg/m3 of white spirit in inspiratory air and under control conditions with exposure to pure air. In another experimental series each subject was tested during exposure to 4,000 mg/m3 of white spirit and under control conditions. Alveolar air samples were taken every fifth minute. No effect on examined functions was observed in the first experimental series. However, a prolonged reaction time and a probably impaired short-term memory was observed in subjects exposed to 4,000 mg/m3. At this concentration of white spirit in inspiratory air an alveolar air concentration was obtaine which corresponded to values obtained in exposure to 2,500 mg/m3 during light exercise.