the antimicrobial activity of $beta$ -hydroxynaphthaldehyde (hna) was tested against 40 different fungal species isolated from deteriorated cotton, textiles, canvas, paper, book bindings, photographic films, leather, footwear and other similar articles. the concentrations 10-100 $mu$ g/ml were tested by poisoned food technique and 60 $mu$ g/ml (0.006) was found to render 100 inhibition in fungal growth. further investigations on mode of action were carried out using aspergillus flavus as a representative fungus the observations on radial growth revealed a gradual decrease from 13.0 to 4.2 mm at 10.0-50.0 $mu$ g/ml concentrations and 28 $degree$ $plus or minus$ 1 $degree$ c. dry weight of mycelium also decreased from 496 to 28.0 mg at the same dosage. after 7 days incubation no growth was seen at 40 and 50 $mu$ g/ml concentrations but, after 12 and 15 days visible growth occurred. the effect of hna on the fungal morphology was loss of colony colour, reduction in head size, shortening and thickening of the mycelium and complete inhibition of sporulation at 50 $mu$ g/ml. the results on the secretion of extra-cellular enzymes, viz. amylase, cellulase, protease and lipase, indicated quantitative reduction with the increasing concentrations of hna. (edited author abstract) 6 refs