17 male subjects are described with foot dermatitis in association with positive patch test reactions to the textile dye Basic Red 46. Chromatographic analysis of the socks of 2 affected patients confirmed the presence of Basic Red 46. Withdrawal of the acrylic blend socks suspected of having been dyed with Basic Red 46 resulted in the improvement of symptoms in 12 of 17 patients (70.6%). However, equivocal or negative patch test results to their own socks were frequently noted in those patients. A highly significant association between the presence of foot dermatitis and a positive Basic Red 46 patch test reaction was noted in 555 patients from a patch test clinic population (P < 0.001). The prevalence of positive patch test reactions to Basic Red 46 was 1.2%. We suggest that patients with foot dermatitis be routinely patch tested for textile dyes. In particular, testing with Basic Red 46 should be considered in those with a history of use of dark-coloured acrylic and/or acrylic blend socks.