The allergen composition of crude extract from sap (latex) of the weeping fig (Ficus benjamina) was investigated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting. The allergenic components were detected by sera from 11 occupationally exposed plant keepers, of whom 7 were non-atopic, and from 9 non-occupationally exposed atopic patients with a positive radio-allergosorbent test to weeping fig. The allergen-antibody complexes were visualized by rabbit anti-IgE and beta-galactosidase-labelled sheep anti-rabbit IgG, using a chromogenic insoluble substrate. A total of 11 allergenic components were identified. Three of them were found to be major allergenic components, identified by more than 50% of the investigated sera. These 3 IgE-binding components had molecular weights of approximately 29,000, 28,000 and 25,000 daltons, respectively. The major allergenic components were denatured by heat in the temperature range of 60-90 degrees C.