Three cases of allergic rhinitis from a vegetable gum, guar gum, have been detected. Two subjects were exposed to fine guar gum powder (Emco Gum 563, Meyhall Chemical AG, Switzerland), an insulator in rubber cables, when opening cables in a power cable laboratory. After 1-2 years' exposure the patients developed rhinitis. Scratch-chamber tests, nasal provocation tests, nasal eosinophilia and a RAST test proved their allergy. A third subject developed allergic rhinitis from another guar gum product (Meyproid 5306, Meyhall Chemical AG) after 2 years' exposure in a paper factory. A positive skin test and nasal provocation test confirmed the diagnosis. A fourth case of possible allergy to guar gum after exposure to Meyproid 5306 in a paper factory is also presented. No final diagnosis was reached in this case (in 1974). The present subjects, only one of whom was atopic, developed allergy within 2 years, although their exposure to guar gum was not especially heavy. Therefore, when handling guar, adequate ventilation facilities should be provided and protective clothing, including a respiratory mask, should be worn.