Under three types of artificial lighting 24 women with chronic agoraphobia and 24 female control subjects assessed their mood and bodily symptoms, and their heart rate was measured. One of the three types of lighting was incandescent. The other two were fluorescent, one pulsating in the conventional manner 100 times per second and the other relatively steady. Both were provided by a single fluorescent lamp controlled from one of two circuits. When exposed to the conventional pulsating fluorescent light under double-blind conditions the agoraphobic group showed a higher heart rate and reported more anomalous visual effects in response to an epileptogenic pattern. Control subjects reported more bodily symptoms under the conventional fluorescent light than under the two other lighting conditions.