Two hundred microorganisms comprising actinomycetes, bacteria, fungi and yeasts were screened for extracellular trehalases by their growth on trehalose in solid and liquid culture.Candida albicans, Gelasinospora retispora and four isolates belonging to the genusFusarium produced extracellular trehalases. The production of trehalase by theFusarium spp. was influenced by the nutrient composition of the medium and the carbon source; of the substrates examined starch produced the highest enzyme titre. Trehalase was an inducible enzyme and was repressed when theFusarium spp. were grown on glucose. The properties of the trehalases from two of theFusarium spp. (isolates MU-105 and TR-8) were typical of non-regulatory trehalases. Activity of several α-glucosidases, an amylase, an invertase and a cellobiase was also demonstrated when the two isolates were grown on trehalose.