Modern biotechnical methods have enabled production of many new types of potentially allergenic proteins. Enzymes have long been known to be respiratory allergens, but relatively few cases of skin allergy have been reported. Here we describe four patients who developed occupational allergic respiratory symptoms, three with bronchial asthma and one with allergic rhinitis, caused by cellulase and/or xylanase enzymes. Each patient also had urticarial symptoms after skin contact with these enzymes. In addition, one of the patients had allergic contact dermatitis from cellulase, and one from xylanase. Allergic contact dermatitis was verified by positive patch tests with the enzymes, and the immediate allergy was revealed by skin prick tests, specific IgE determinations (RAST) and RAST-inhibition tests. All patients had positive RASTs to both cellulase and xylanase. In the RAST inhibition test 20 μ1 of cellulase brought about a 94% inhibition, indicating the specificity of the RAST. Xylanase (20 μl, 5% w/v) gave an 92% inhibition of cellulase RAST, indicating cross-reactivity between cellulase and xylanase. Three patients have been able to continue at their previous places of work, but at different worksites. One of the patients requires continuous medication for asthma and had to change her job because of persistent symptoms.