In a study of 274 women with malignant melanoma, aged 18--54 years, and 549 matched controls in New South Wales, Australia, reported exposure to fluorescent light at work was associated with a doubling of melanoma risk (relative risk [RR] = 2.1; 95% confidence limits 1.32--3.32). The risk grew with increasing duration of exposure to fluorescent light and was higher in women who had worked mainly in offices (RR = 2.6) than in women whose main place of work was indoors but not in offices (RR = 1.8). The findings could not be explained by the differences in histories of sunlight exposure, in skin or hair colour, or in any other factor. There was a relative excess of lesions on the trunk in the group exposed to fluorescent light at work. 27 men with melanoma and 35 similarly aged controls were studied, and a significant increase in risk was also found: the RB in those exposed for greater than or equal to 10 years compared with those exposed for less than 10 years was 4.4 (95% confidence limits 1.1--17.5). Such an association has not been reported before, but it is plausible and could explain many of the paradoxical features of the epidemiology of melanoma. Until more data accumulate it must, however, be viewed cautiously.