Streptomyces amakusaensis KO-8119, a soil isolate, was found to produce a series of new anticoccidial compounds. Four active compounds, designated as cytosaminomycins A, B, C and D, were isolated from the fermentation broth of the producing strain by solvent extraction, silica gel column chromatography and preparative HPLC. Cytosaminomycins inhibited the growth of Eimeria tenella in an in vitro assay system using primary chicken embryonic cells as a host. No schizont in the cells was observed at concentrations ranging from 0.3 to 0.6 microgram/ml for cytosaminomycins A, B and C, and at 2.5 micrograms/ml for cytosaminomycin D.