Previous studies suggest that reactive dyes can induce IgE mediated bronchoconstrictions. To evaluate the significance of specific IgE and IgG antibodies in workers exposed to reactive dyes, we studied the prevalence of Black GR-specific IgG by enzyme linked immunosorbent assay, as well as Black GR-specific IgE by RAST, in 176 workers employed in 1 reactive dye factory and 4 neighboring factories. Six employees of reactive dye asthma who were working in factories near the reactive dye factories were noted. The prevalence of specific IgE antibodies in the neighboring factories was higher than in that of the reactive dye factory. The prevalence of specific IgG was highest in the reactive dye factory, and those of the neighboring factories were markedly lower. It was suggested that IgE mediated sensitization to reactive dye could have occurred in employees who were working in neighboring factories, and the prevalence of reactive dye-specific IgG antibody could be used as an in direct method of assessing the exposure of workers to reactive dye.