A 134 kDa, calcium-independent, chitin-binding lectin called chitovibrin is secreted by marine bacteria of the genus Vibnio. The secretion of chitovibrin is inducible by chitin or chitin-oligomers. Chitovibrin shows no apparent enzymatic activity, but has a strong affinity for chitin and for chito-oligomers dp9 and larger. The protein has an isoelectric pH of 3.6, shows thermal tolerance, binds chitin with an optimum at pH 6 and is active in 0-4 M NaCl. Chitovibrin is useful as a stain for fungi and other chitin-containing organisms. Chitovibrin may be used to detect the presence of chitin, particularly in diagnosing fungal infections in humans, animals, and plant materials. Fungal infections are a particular problem in immunocompromised hosts such as AIDS patients and bone marrow transplant patients, because they can cause opportunistic infections. The chitovibrin diagnostic method allows the convenient, broad spectrum diagnosis of fungal infections in tissue samples or in body fluids. Other, smaller polypeptide fragments of chitovibrin will exhibit similar chitin-binding properties, and could be used in coupling to detection systems.