Four patients with occupational asthma were studied. All patients were exposed to African maple dust and two of them were also exposed to Ramin dust. Skin tests and bronchial provocation tests with African maple extracts revealed an immediate response in all patients, and the same tests performed with Ramin extracts again revealed an immediate reaction in either exposed or non-exposed patients to Ramin wood dust. Specific IgE antibodies against African maple extracts were demonstrated in all patients as measured by a reverse enzyme immunoassay. Cross reactivity between both woods was demonstrated by a reverse enzyme immunoassay inhibition study. Unexposed persons and exposed asymptomatic workers did not exhibit reactivity to both woods in any of the tests listed above. To the best of our knowledge, this is the first article in which occupational asthma due to Ramin is defined, and cross sensitivity between two different woods is demonstrated.