1-[2-(2,4-Dichlorophenyl)-2-(2-propenyloxy)-ethyl]-1H-imidazole (imazalil) base and different salts were tested in vitro on various pathogenic fungi and bacteria; in vivo on guinea-pigs, rats and turkeys experimentally infected with dermatophytes and Candida albicans. In vitro the dermatophytes were the most sensitive. The plant-pathogenic fungi were more sensitive to the base than to the salts. The antibacterial activity was low. The in vivo antifungal activity was high for the dermatophytes and rather low for Candida. The acute, subacute and chronic toxicity studies in rats and dogs showed that imazalil wa a well tolerated substance. Ocular and dermal irritation were not seen at therapeutic doses. Fertility and reproductive capacity were not affected and embryotoxicity and teratogenicity were not seen. No mutagenic or cancerogenic potential was found.