Abstract: The present invention relates to anthelmintic preparations containing 4-(4-nitroanilino)-phenylisothiocyanate having a median of particle size of at most 10 .mu.m, particularly at most 5 .mu.m, and to the treatment of infections by parasitic helminthes, especially to the treatment of warm-blooded animals affected by shistosomiasis, hookworm infestation of filariasis, by administration of the preparations named above. Specific embodiments are suspensions of the active substance in triglycerides of medium saturated fatty acids, and mixtures of the active substance with a starch, particularly with maize starch.