One hundred and one strains of bacteria from environmental and clinical sources, most of which were Gram negative, were tested for n-acetyl-Beta-D-glucosaminidase activity using a filter paper spot test with 4-methylumbelliferyl-N-acetyl-Beta-D-glucosaminide (4-MNABetaG) as substrate. The results were compared to those obtained by a conventional plate method for chitinase activity using colloidal chitin as substrate. There was excellent agreement in results for both methods. The filter paper spot test with 4-MNABeta has the advantages of being rapid, simple-to-perform and inexpensive. This method should be adaptable to a wider range of microorganisms, particularly those with unusual growth requirements. (Copyright (c) 1987 American Society for Microbiology.)