Reactive dyes have been widely used in recent years. This paper reports nine cases of immediate type occupational asthma to reactive dyes in one dye industry. All patients had had asthmatic symptoms, four had had rhinitis and they had worked for 6 to 25 months. Skin prick tests with reactive dyes were positive and bronchoprovocation tests also produced immediate or dual types of bronchoconstriction. We used the radioallergosorbent test (RAST) technique with nitrocellulose filter paper as a solid phase to detect specific IgE to four reactive dye-human serum albumin conjugates. High specific IgE binding was found in eight asthmatic workers compared with 13 negative controls. The RAST inhibition test revealed that there was no immunological cross-reactivity between 4 reactive dyes. These results suggested that the mechanism of their asthmatic symptoms was immunological, mostly an IgE-mediate reaction.