The studies on different concentrations of malathion, thiodan, mancozeb, captafol, tridemorph, carbendazim, paraquat and 2, 4-dichlorophenoxy butyric acid on the sporulation of 18 species of aquatic hyphomycetes have revealed that these chemicals had no inhibitory effect on the sporulation upto 5 mg 1(-1). At higher concentrations their effect varied. The tolerance of the organisms to the chemicals is believed to be substrate dependant. The germination of conidia of Campylospora chaetocladia, Flabellospora verticillata, Flagellospora penicilliodes, Helicosporium sp., Lunulospora curvula and Wiesneriomyces javanicus was not inhibited upto 1 mg 1(-1) in all the chemicals. Above this concentration the per cent germination of conidia decreased with increase in the concentration.