Seven patients with occupational asthma caused by a chemical, tetrachlorophthalic anhydride (TCPA), left their work in 1980. They have subsequently avoided TCPA exposure and have been followed until 1985. One patient died in 1981. The six living patients reported continuing symptoms suggestive of asthma, and five who were studied in 1985 demonstrated mild bronchial hyperresponsiveness (histamine concentration provoking a 20% fall in FEV1 range 2.7 to 12.5 mg/ml). Specific IgE antibody to TCPA conjugated with human serum albumin was measured by a radioallergosorbent test and detected in all patients. After avoidance of exposure, specific IgE fell exponentially with a half-life of 1 year. Specific IgE was still detectable in 1985, and throughout the follow-up period, prick tests with the conjugate elicited immediate skin responses. In 1981 four patients had inhalation tests with TCPA, and specific IgE rose afterward and then fell again.